diff --git a/lib/api/user_api.dart b/lib/api/user_api.dart
index 13fb12cb..cc40b06e 100755
--- a/lib/api/user_api.dart
+++ b/lib/api/user_api.dart
@@ -77,7 +77,7 @@ class UserAPI {
     if (uid == null) {
       return currentUser;
     } else {
-      return NetUtils.getWithCookieAndHeaderSet(
+      return NetUtils.getWithCookieAndHeaderSet<void>(
         API.userInfo,
         data: <String, dynamic>{'uid': uid},
       );
diff --git a/lib/constants/constants.dart b/lib/constants/constants.dart
index a67c2fdb..23c17ad2 100644
--- a/lib/constants/constants.dart
+++ b/lib/constants/constants.dart
@@ -10,6 +10,7 @@ import 'package:openjmu/constants/constants.dart';
 export 'package:dartx/dartx.dart';
 export 'package:dio/dio.dart' show Response;
 export 'package:ff_annotation_route/ff_annotation_route.dart' show FFRoute, PageRouteType;
+export 'package:hive/hive.dart' show Box;
 export 'package:oktoast/oktoast.dart' hide showToast;
 export 'package:pedantic/pedantic.dart';
 export 'package:url_launcher/url_launcher.dart';
diff --git a/lib/openjmu_route_helper.dart b/lib/openjmu_route_helper.dart
index 211e8693..179ccc19 100644
--- a/lib/openjmu_route_helper.dart
+++ b/lib/openjmu_route_helper.dart
@@ -12,40 +12,42 @@ import 'package:flutter/widgets.dart';
 import 'openjmu_route.dart';
 
 class FFNavigatorObserver extends NavigatorObserver {
-  final RouteChange routeChange;
-
   FFNavigatorObserver({this.routeChange});
 
+  final RouteChange routeChange;
+
   @override
-  void didPop(Route route, Route previousRoute) {
+  void didPop(Route<dynamic> route, Route<dynamic> previousRoute) {
     super.didPop(route, previousRoute);
     _didRouteChange(previousRoute, route);
   }
 
   @override
-  void didPush(Route route, Route previousRoute) {
+  void didPush(Route<dynamic> route, Route<dynamic> previousRoute) {
     super.didPush(route, previousRoute);
     _didRouteChange(route, previousRoute);
   }
 
   @override
-  void didRemove(Route route, Route previousRoute) {
+  void didRemove(Route<dynamic> route, Route<dynamic> previousRoute) {
     super.didRemove(route, previousRoute);
     _didRouteChange(previousRoute, route);
   }
 
   @override
-  void didReplace({Route newRoute, Route oldRoute}) {
+  void didReplace({Route<dynamic> newRoute, Route<dynamic> oldRoute}) {
     super.didReplace(newRoute: newRoute, oldRoute: oldRoute);
     _didRouteChange(newRoute, oldRoute);
   }
 
-  void _didRouteChange(Route newRoute, Route oldRoute) {
+  void _didRouteChange(Route<dynamic> newRoute, Route<dynamic> oldRoute) {
     routeChange?.call(newRoute?.settings, oldRoute?.settings);
   }
 
-  FFRouteSettings getFFRouteSettings(Route route) {
-    if (route?.settings is FFRouteSettings) return route.settings;
+  FFRouteSettings getFFRouteSettings(Route<dynamic> route) {
+    if (route?.settings is FFRouteSettings) {
+      return route.settings as FFRouteSettings;
+    }
     return null;
   }
 }
@@ -91,9 +93,9 @@ Widget _defaultTransitionsBuilder(
 }
 
 Route<dynamic> onGenerateRouteHelper(RouteSettings settings, {Widget notFoundFallback}) {
-  final routeResult = getRouteResult(
+  final RouteResult routeResult = getRouteResult(
     name: settings.name,
-    arguments: settings.arguments,
+    arguments: settings.arguments as Map<String, dynamic>,
   );
   if (routeResult.showStatusBar != null || routeResult.routeName != null) {
     settings = FFRouteSettings(
@@ -104,37 +106,38 @@ Route<dynamic> onGenerateRouteHelper(RouteSettings settings, {Widget notFoundFal
       showStatusBar: routeResult.showStatusBar,
     );
   }
-  final page = routeResult.widget ??
+  final Widget page = routeResult.widget ??
       notFoundFallback ??
-      Center(child: Text("${settings.name}\npage not found."));
+      Center(child: Text('${settings.name}\npage not found.'));
 
   if (settings?.arguments is Map<String, dynamic>) {
-    RouteBuilder builder = (settings.arguments as Map<String, dynamic>)['routeBuilder'];
-    if (builder != null) return builder(page);
+    final RouteBuilder builder =
+        (settings.arguments as Map<String, dynamic>)['routeBuilder'] as RouteBuilder;
+    if (builder != null) {
+      return builder(page);
+    }
   }
 
   switch (routeResult.pageRouteType) {
     case PageRouteType.material:
-      return MaterialPageRoute(settings: settings, builder: (_) => page);
+      return MaterialPageRoute<dynamic>(settings: settings, builder: (_) => page);
     case PageRouteType.cupertino:
-      return CupertinoPageRoute(settings: settings, builder: (_) => page);
+      return CupertinoPageRoute<dynamic>(settings: settings, builder: (_) => page);
     case PageRouteType.transparent:
-      return FFTransparentPageRoute(
+      return FFTransparentPageRoute<dynamic>(
         settings: settings,
         pageBuilder: (_, __, ___) => page,
       );
     default:
       return Platform.isIOS
-          ? CupertinoPageRoute(settings: settings, builder: (_) => page)
-          : MaterialPageRoute(settings: settings, builder: (_) => page);
+          ? CupertinoPageRoute<dynamic>(settings: settings, builder: (_) => page)
+          : MaterialPageRoute<dynamic>(settings: settings, builder: (_) => page);
   }
 }
 
-typedef RouteBuilder = PageRoute Function(Widget page);
+typedef RouteBuilder = PageRoute<dynamic> Function(Widget page);
 
 class FFRouteSettings extends RouteSettings {
-  final String routeName;
-  final bool showStatusBar;
   const FFRouteSettings({
     this.routeName,
     this.showStatusBar,
@@ -142,4 +145,7 @@ class FFRouteSettings extends RouteSettings {
     bool isInitialRoute = false,
     Object arguments,
   }) : super(name: name, isInitialRoute: isInitialRoute, arguments: arguments);
+
+  final String routeName;
+  final bool showStatusBar;
 }
diff --git a/lib/pages/login_page.dart b/lib/pages/login_page.dart
index dd1468a1..31e7fdb8 100755
--- a/lib/pages/login_page.dart
+++ b/lib/pages/login_page.dart
@@ -443,28 +443,33 @@ class LoginPageState extends State<LoginPage> with SingleTickerProviderStateMixi
       );
 
   void loginButtonPressed(context) {
-    if (_formKey.currentState.validate()) {
-      _formKey.currentState.save();
-      setState(() {
-        _login = true;
-      });
-      DataUtils.login(_username, _password).then((result) {
-        if (result) {
-          navigatorState.pushNamedAndRemoveUntil(
-            Routes.OPENJMU_HOME,
-            (_) => false,
-            arguments: {'initAction': null},
-          );
-        } else {
+    try {
+      if (_formKey.currentState.validate()) {
+        _formKey.currentState.save();
+        setState(() {
+          _login = true;
+        });
+        DataUtils.login(_username, _password).then((result) {
+          if (result) {
+            navigatorState.pushNamedAndRemoveUntil(
+              Routes.OPENJMU_HOME,
+              (_) => false,
+              arguments: {'initAction': null},
+            );
+          } else {
+            _login = false;
+            if (mounted) setState(() {});
+          }
+        }).catchError((e) {
+          debugPrint('Failed when login: $e');
+          showCenterErrorToast('登录失败');
           _login = false;
           if (mounted) setState(() {});
-        }
-      }).catchError((e) {
-        debugPrint('Failed when login: $e');
-        showToast('登录失败');
-        _login = false;
-        if (mounted) setState(() {});
-      });
+        });
+      }
+    } catch (e) {
+      debugPrint('Failed when login: $e');
+      showCenterErrorToast('登录失败');
     }
   }
 
diff --git a/lib/pages/user/user_page.dart b/lib/pages/user/user_page.dart
index 475b5a6e..21a12954 100755
--- a/lib/pages/user/user_page.dart
+++ b/lib/pages/user/user_page.dart
@@ -469,7 +469,10 @@ class _UserPageState extends State<UserPage>
                 'pics': [
                   ImageBean(
                     id: widget.uid,
-                    imageUrl: '${API.userAvatar}?uid=${widget.uid}&size=f640',
+                    imageUrl: '${API.userAvatar}?'
+                        'uid=${widget.uid}'
+                        '&size=f640'
+                        '&_t=${UserAPI.avatarLastModified}',
                   ),
                 ],
                 'heroPrefix': 'user-page-avatar-',
diff --git a/lib/providers/settings_provider.dart b/lib/providers/settings_provider.dart
index a12c6d98..e8dcb509 100644
--- a/lib/providers/settings_provider.dart
+++ b/lib/providers/settings_provider.dart
@@ -10,7 +10,7 @@ import 'package:openjmu/constants/constants.dart';
 
 class SettingsProvider extends ChangeNotifier {
   /// For test page.
-  /// TODO: Set this to false before release.
+  /// Set this to [false] before release.
   bool _debug = !kReleaseMode && false;
   bool get debug => _debug;
   set debug(bool value) {
@@ -26,10 +26,10 @@ class SettingsProvider extends ChangeNotifier {
     notifyListeners();
   }
 
-  List<int> _homeStartUpIndex = [0, 0, 0];
+  List<int> _homeStartUpIndex = <int>[0, 0, 0];
   List<int> get homeStartUpIndex => _homeStartUpIndex;
   set homeStartUpIndex(List<int> value) {
-    _homeStartUpIndex = List.from(value);
+    _homeStartUpIndex = List<int>.from(value);
     notifyListeners();
   }
 
@@ -72,12 +72,14 @@ class SettingsProvider extends ChangeNotifier {
   bool get launchFromSystemBrowser => _launchFromSystemBrowser;
   set launchFromSystemBrowser(bool value) {
     assert(value != null);
-    if (_launchFromSystemBrowser == value) return;
+    if (_launchFromSystemBrowser == value) {
+      return;
+    }
     _launchFromSystemBrowser = value;
     notifyListeners();
   }
 
-  final fontScaleRange = <double>[0.6, 1.4];
+  final List<double> fontScaleRange = <double>[0.6, 1.4];
   double _fontScale = 1.0;
   double get fontScale => _fontScale;
   set fontScale(double value) {
@@ -99,7 +101,7 @@ class SettingsProvider extends ChangeNotifier {
   void reset() {
     _fontScale = 1.0;
     _homeSplashIndex = 0;
-    _homeStartUpIndex = [0, 0, 0];
+    _homeStartUpIndex = <int>[0, 0, 0];
     _newAppCenterIcon = false;
     _hideShieldPost = true;
     _launchFromSystemBrowser = false;
diff --git a/lib/utils/hive_field_utils.dart b/lib/utils/hive_field_utils.dart
index c93cf58e..c5f3985a 100644
--- a/lib/utils/hive_field_utils.dart
+++ b/lib/utils/hive_field_utils.dart
@@ -12,116 +12,116 @@ class HiveFieldUtils {
         listen: false,
       );
 
-  static final _box = HiveBoxes.settingsBox;
+  static final Box<dynamic> _box = HiveBoxes.settingsBox;
 
-  static final String brightnessDark = 'theme_brightness';
-  static final String amoledDark = 'theme_AMOLEDDark';
-  static final String colorThemeIndex = 'theme_colorThemeIndex';
-  static final String brightnessPlatform = 'theme_brightness_platform';
-  static final String settingHomeSplashIndex = 'setting_home_splash_index';
-  static final String settingHomeStartUpIndex = 'setting_home_startup_index';
+  static const String brightnessDark = 'theme_brightness';
+  static const String amoledDark = 'theme_AMOLEDDark';
+  static const String colorThemeIndex = 'theme_colorThemeIndex';
+  static const String brightnessPlatform = 'theme_brightness_platform';
+  static const String settingHomeSplashIndex = 'setting_home_splash_index';
+  static const String settingHomeStartUpIndex = 'setting_home_startup_index';
 
-  static final String settingFontScale = 'setting_font_scale';
-  static final String settingNewIcons = 'setting_new_icons';
-  static final String settingHideShieldPost = 'setting_hide_shield_post';
-  static final String settingLaunchFromSystemBrowser = 'setting_launch_from_system_browser';
+  static const String settingFontScale = 'setting_font_scale';
+  static const String settingNewIcons = 'setting_new_icons';
+  static const String settingHideShieldPost = 'setting_hide_shield_post';
+  static const String settingLaunchFromSystemBrowser = 'setting_launch_from_system_browser';
 
-  static final String deviceUuid = 'device_uuid';
-  static final String devicePushToken = 'device_push_token';
+  static const String deviceUuid = 'device_uuid';
+  static const String devicePushToken = 'device_push_token';
 
   /// 获取设置的主题色
-  static int getColorThemeIndex() => _box?.get(colorThemeIndex) ?? 0;
+  static int getColorThemeIndex() => _box?.get(colorThemeIndex) as int ?? 0;
 
   /// 获取设置的夜间模式
-  static bool getBrightnessDark() => _box?.get(brightnessDark) ?? false;
+  static bool getBrightnessDark() => _box?.get(brightnessDark) as bool ?? false;
 
   /// 获取设置的AMOLED夜间模式
-  static bool getAMOLEDDark() => _box?.get(amoledDark) ?? false;
+  static bool getAMOLEDDark() => _box?.get(amoledDark) as bool ?? false;
 
   /// 获取设置的跟随系统夜间模式
-  static bool getBrightnessPlatform() => _box?.get(brightnessPlatform) ?? true;
+  static bool getBrightnessPlatform() => _box?.get(brightnessPlatform) as bool ?? true;
 
   /// 设置选择的主题色
-  static Future setColorTheme(int value) async => await _box?.put(colorThemeIndex, value);
+  static Future<void> setColorTheme(int value) async => await _box?.put(colorThemeIndex, value);
 
   /// 设置选择的夜间模式
-  static Future setBrightnessDark(bool value) async => await _box?.put(brightnessDark, value);
+  static Future<void> setBrightnessDark(bool value) async => await _box?.put(brightnessDark, value);
 
   /// 设置AMOLED夜间模式
-  static Future setAMOLEDDark(bool value) async => await _box?.put(amoledDark, value);
+  static Future<void> setAMOLEDDark(bool value) async => await _box?.put(amoledDark, value);
 
   /// 设置跟随系统的夜间模式
-  static Future setBrightnessPlatform(bool value) async =>
+  static Future<void> setBrightnessPlatform(bool value) async =>
       await _box?.put(brightnessPlatform, value);
 
   /// 获取默认启动页index
-  static int getHomeSplashIndex() => _box?.get(settingHomeSplashIndex);
+  static int getHomeSplashIndex() => _box?.get(settingHomeSplashIndex) as int;
 
   /// 获取默认各页启动index
-  static List getHomeStartUpIndex() => _box?.get(settingHomeStartUpIndex)?.cast<int>();
+  static List<int> getHomeStartUpIndex() => _box?.get(settingHomeStartUpIndex) as List<int>;
 
   /// 获取字体缩放设置
-  static double getFontScale() => _box?.get(settingFontScale);
+  static double getFontScale() => _box?.get(settingFontScale) as double;
 
   /// 获取新图标是否开启
-  static bool getEnabledNewAppsIcon() => _box?.get(settingNewIcons);
+  static bool getEnabledNewAppsIcon() => _box?.get(settingNewIcons) as bool;
 
   /// 获取是否隐藏被屏蔽的动态
-  static bool getEnabledHideShieldPost() => _box?.get(settingHideShieldPost);
+  static bool getEnabledHideShieldPost() => _box?.get(settingHideShieldPost) as bool;
 
   /// 获取是否通过系统浏览器打开网页
-  static bool getLaunchFromSystemBrowser() => _box?.get(settingLaunchFromSystemBrowser);
+  static bool getLaunchFromSystemBrowser() => _box?.get(settingLaunchFromSystemBrowser) as bool;
 
   /// 设置首页的初始页
-  static Future<Null> setHomeSplashIndex(int index) async {
+  static Future<void> setHomeSplashIndex(int index) async {
     provider.homeSplashIndex = index;
     await _box?.put(settingHomeSplashIndex, index);
   }
 
   /// 设置首页各子页的初始页
-  static Future<Null> setHomeStartUpIndex(List<int> indexList) async {
+  static Future<void> setHomeStartUpIndex(List<int> indexList) async {
     provider.homeStartUpIndex = indexList;
     await _box?.put(settingHomeStartUpIndex, indexList);
   }
 
   /// 设置字体缩放
-  static Future<Null> setFontScale(double scale) async {
+  static Future<void> setFontScale(double scale) async {
     provider.fontScale = scale;
     await _box?.put(settingFontScale, scale);
   }
 
   /// 设置是否启用新应用图标
-  static Future<Null> setEnabledNewAppsIcon(bool enable) async {
+  static Future<void> setEnabledNewAppsIcon(bool enable) async {
     provider.newAppCenterIcon = enable;
     await _box?.put(settingNewIcons, enable);
   }
 
   /// 设置是否隐藏被屏蔽的动态
-  static Future<Null> setEnabledHideShieldPost(bool enable) async {
+  static Future<void> setEnabledHideShieldPost(bool enable) async {
     provider.hideShieldPost = enable;
     await _box?.put(settingHideShieldPost, enable);
   }
 
   /// 设置是否通过系统浏览器打开网页
-  static Future<Null> setLaunchFromSystemBrowser(bool enable) async {
+  static Future<void> setLaunchFromSystemBrowser(bool enable) async {
     provider.launchFromSystemBrowser = enable;
     await _box?.put(settingLaunchFromSystemBrowser, enable);
   }
 
   /// 获取设备PushToken
-  static String getDevicePushToken() => _box?.get(devicePushToken);
+  static String getDevicePushToken() => _box?.get(devicePushToken) as String;
 
   /// 获取设备Uuid
-  static String getDeviceUuid() => _box?.get(deviceUuid);
+  static String getDeviceUuid() => _box?.get(deviceUuid) as String;
 
   /// 写入PushToken
-  static Future<Null> setDevicePushToken(String value) async {
+  static Future<void> setDevicePushToken(String value) async {
     DeviceUtils.devicePushToken = value;
     await _box?.put(devicePushToken, value);
   }
 
   /// 写入uuid
-  static Future<Null> setDeviceUuid(String value) async {
+  static Future<void> setDeviceUuid(String value) async {
     DeviceUtils.deviceUuid = value;
     await _box?.put(deviceUuid, value);
   }
diff --git a/lib/utils/net_utils.dart b/lib/utils/net_utils.dart
index 9230a51b..8bb02f20 100755
--- a/lib/utils/net_utils.dart
+++ b/lib/utils/net_utils.dart
@@ -112,9 +112,9 @@ class NetUtils {
 
   static Future<Response<T>> getWithCookieAndHeaderSet<T>(
     String url, {
-    data,
-    cookies,
-    headers,
+    Map<String, dynamic> data,
+    List<Cookie> cookies,
+    Map<String, dynamic> headers,
   }) async =>
       await dio.get<T>(
         url,
diff --git a/lib/widgets/dialogs/confirmation_dialog.dart b/lib/widgets/dialogs/confirmation_dialog.dart
index 799a79cf..6a5ff5be 100644
--- a/lib/widgets/dialogs/confirmation_dialog.dart
+++ b/lib/widgets/dialogs/confirmation_dialog.dart
@@ -10,19 +10,6 @@ import 'package:extended_text/extended_text.dart';
 import 'package:extended_text_library/extended_text_library.dart';
 
 class ConfirmationDialog extends StatelessWidget {
-  final String title;
-  final bool centerTitle;
-  final Widget child;
-  final String content;
-  final EdgeInsetsGeometry contentPadding;
-  final TextAlign contentAlignment;
-  final Color backgroundColor;
-  final bool showConfirm;
-  final String confirmLabel;
-  final String cancelLabel;
-  final VoidCallback onConfirm;
-  final VoidCallback onCancel;
-
   const ConfirmationDialog({
     Key key,
     this.title,
@@ -43,8 +30,21 @@ class ConfirmationDialog extends StatelessWidget {
         ),
         super(key: key);
 
+  final String title;
+  final bool centerTitle;
+  final Widget child;
+  final String content;
+  final EdgeInsetsGeometry contentPadding;
+  final TextAlign contentAlignment;
+  final Color backgroundColor;
+  final bool showConfirm;
+  final String confirmLabel;
+  final String cancelLabel;
+  final VoidCallback onConfirm;
+  final VoidCallback onCancel;
+
   static Future<bool> show(
-    context, {
+    BuildContext context, {
     String title,
     bool centerTitle = true,
     Widget child,
@@ -72,7 +72,7 @@ class ConfirmationDialog extends StatelessWidget {
         false;
   }
 
-  Widget titleWidget(context) => Row(
+  Widget titleWidget(BuildContext context) => Row(
         mainAxisAlignment: centerTitle ? MainAxisAlignment.center : MainAxisAlignment.start,
         children: <Widget>[
           Text(
@@ -84,7 +84,7 @@ class ConfirmationDialog extends StatelessWidget {
         ],
       );
 
-  Widget confirmButton(context) {
+  Widget confirmButton(BuildContext context) {
     return Expanded(
       flex: 5,
       child: MaterialButton(
@@ -111,7 +111,7 @@ class ConfirmationDialog extends StatelessWidget {
     );
   }
 
-  Widget cancelButton(context) {
+  Widget cancelButton(BuildContext context) {
     return Expanded(
       flex: 5,
       child: MaterialButton(
@@ -167,25 +167,25 @@ class ConfirmationDialog extends StatelessWidget {
               mainAxisSize: MainAxisSize.min,
               children: <Widget>[
                 if (title != null) titleWidget(context),
-                child != null
-                    ? child
-                    : Padding(
-                        padding:
-                            contentPadding ?? EdgeInsets.symmetric(vertical: suSetHeight(20.0)),
-                        child: ExtendedText(
-                          '$content',
-                          style: TextStyle(fontSize: suSetSp(20.0), fontWeight: FontWeight.normal),
-                          textAlign: contentAlignment,
-                          specialTextSpanBuilder: RegExpSpecialTextSpanBuilder(),
-                          onSpecialTextTap: (data) {
-                            API.launchWeb(url: data['content'], title: '网页链接');
-                          },
-                        ),
-                      ),
+                if (child != null)
+                  child
+                else
+                  Padding(
+                    padding: contentPadding ?? EdgeInsets.symmetric(vertical: suSetHeight(20.0)),
+                    child: ExtendedText(
+                      '$content',
+                      style: TextStyle(fontSize: suSetSp(20.0), fontWeight: FontWeight.normal),
+                      textAlign: contentAlignment,
+                      specialTextSpanBuilder: RegExpSpecialTextSpanBuilder(),
+                      onSpecialTextTap: (dynamic data) {
+                        API.launchWeb(url: data['content'] as String, title: '网页链接');
+                      },
+                    ),
+                  ),
                 Row(
                   children: <Widget>[
                     if (showConfirm) confirmButton(context),
-                    if (showConfirm) Spacer(flex: 1),
+                    if (showConfirm) const Spacer(flex: 1),
                     cancelButton(context),
                   ],
                 ),
@@ -212,7 +212,7 @@ class LinkText extends SpecialText {
       style: textStyle?.copyWith(decoration: TextDecoration.underline),
       recognizer: TapGestureRecognizer()
         ..onTap = () {
-          final data = {'content': toString()};
+          final Map<String, dynamic> data = <String, dynamic>{'content': toString()};
           if (onTap != null) onTap(data);
         },
     );
diff --git a/lib/widgets/dialogs/edit_signature_dialog.dart b/lib/widgets/dialogs/edit_signature_dialog.dart
index fcfcb30b..66651dcd 100755
--- a/lib/widgets/dialogs/edit_signature_dialog.dart
+++ b/lib/widgets/dialogs/edit_signature_dialog.dart
@@ -35,20 +35,20 @@ class EditSignatureDialogState extends State<EditSignatureDialog> {
       });
   }
 
-  void updateSignature(context) {
+  void updateSignature(BuildContext context) {
     Navigator.of(context).pop();
-    final _loadingDialogController = LoadingDialogController();
+    final LoadingDialogController _loadingDialogController = LoadingDialogController();
     LoadingDialog.show(
       context,
       text: '正在更新签名',
       controller: _loadingDialogController,
       isGlobal: false,
     );
-    UserAPI.setSignature(_textEditingController.text).then((response) {
+    UserAPI.setSignature(_textEditingController.text).then((dynamic _) {
       _loadingDialogController.changeState('success', '签名更新成功');
       UserAPI.currentUser.signature = _textEditingController.text;
       Instances.eventBus.fire(SignatureUpdatedEvent(_textEditingController.text));
-    }).catchError((e) {
+    }).catchError((dynamic e) {
       debugPrint(e.toString());
       _loadingDialogController.changeState('failed', '签名更新失败');
     });
@@ -102,9 +102,7 @@ class EditSignatureDialogState extends State<EditSignatureDialog> {
                           borderSide: BorderSide(color: Colors.grey[850]),
                         ),
                         hintText: UserAPI.currentUser.signature ?? '快来填写你的签名吧~',
-                        hintStyle: TextStyle(
-                          textBaseline: TextBaseline.alphabetic,
-                        ),
+                        hintStyle: const TextStyle(textBaseline: TextBaseline.alphabetic),
                       ),
                       cursorColor: currentThemeColor,
                     ),
diff --git a/lib/widgets/dialogs/forward_positioned.dart b/lib/widgets/dialogs/forward_positioned.dart
index 3e360763..06731d1e 100755
--- a/lib/widgets/dialogs/forward_positioned.dart
+++ b/lib/widgets/dialogs/forward_positioned.dart
@@ -1,6 +1,6 @@
+import 'dart:async';
 import 'dart:io';
 import 'dart:math';
-import 'dart:async';
 
 import 'package:flutter/material.dart';
 import 'package:flutter/cupertino.dart';
@@ -21,20 +21,20 @@ import 'package:openjmu/widgets/dialogs/mention_people_dialog.dart';
   pageRouteType: PageRouteType.transparent,
 )
 class ForwardPositioned extends StatefulWidget {
-  final Post post;
-
   const ForwardPositioned({
     Key key,
     @required this.post,
   }) : super(key: key);
 
+  final Post post;
+
   @override
   State<StatefulWidget> createState() => ForwardPositionedState();
 }
 
 class ForwardPositionedState extends State<ForwardPositioned> {
-  final _forwardController = TextEditingController();
-  final _focusNode = FocusNode();
+  final TextEditingController _forwardController = TextEditingController();
+  final FocusNode _focusNode = FocusNode();
   File _image;
   int _imageID;
 
@@ -59,15 +59,13 @@ class ForwardPositionedState extends State<ForwardPositioned> {
 //    if (mounted) setState(() {});
 //  }
 
-  FormData createForm(File file) => FormData.from({
+  FormData createForm(File file) => FormData.from(<String, dynamic>{
         'image': UploadFileInfo(file, path.basename(file.path)),
         'image_type': 0,
       });
 
-  Future getImageRequest(FormData formData) async => NetUtils.postWithCookieAndHeaderSet(
-        API.postUploadImage,
-        data: formData,
-      );
+  Future<Response<dynamic>> getImageRequest(FormData formData) async =>
+      NetUtils.postWithCookieAndHeaderSet<void>(API.postUploadImage, data: formData);
 
   Widget get textField => ExtendedTextField(
         specialTextSpanBuilder: StackSpecialTextFieldSpanBuilder(),
@@ -76,23 +74,16 @@ class ForwardPositionedState extends State<ForwardPositioned> {
         decoration: InputDecoration(
           contentPadding: EdgeInsets.all(suSetWidth(16.0)),
           border: OutlineInputBorder(
-            borderSide: BorderSide(
-              color: currentThemeColor,
-            ),
+            borderSide: BorderSide(color: currentThemeColor),
           ),
           focusedBorder: OutlineInputBorder(
-            borderSide: BorderSide(
-              color: currentThemeColor,
-            ),
+            borderSide: BorderSide(color: currentThemeColor),
           ),
           suffixIcon: _image != null
               ? Container(
                   margin: EdgeInsets.only(right: suSetWidth(16.0)),
                   width: suSetWidth(70.0),
-                  child: Image.file(
-                    _image,
-                    fit: BoxFit.cover,
-                  ),
+                  child: Image.file(_image, fit: BoxFit.cover),
                 )
               : null,
         ),
@@ -106,7 +97,7 @@ class ForwardPositionedState extends State<ForwardPositioned> {
         maxLines: 3,
       );
 
-  Future<void> _request(context) async {
+  Future<void> _request(BuildContext context) async {
     setState(() {
       _forwarding = true;
     });
@@ -115,8 +106,9 @@ class ForwardPositionedState extends State<ForwardPositioned> {
 
     /// Sending image if it exist.
     if (_image != null) {
-      final Map<String, dynamic> data = (await getImageRequest(createForm(_image))).data;
-      _imageID = int.parse(data['image_id']);
+      final Map<String, dynamic> data =
+          (await getImageRequest(createForm(_image))).data as Map<String, dynamic>;
+      _imageID = int.parse(data['image_id'] as String);
       content += ' |$_imageID| ';
     }
 
@@ -137,22 +129,26 @@ class ForwardPositionedState extends State<ForwardPositioned> {
       } else {
         showToast('转发失败');
       }
-      if (mounted) setState(() {});
+      if (mounted) {
+        setState(() {});
+      }
     }
   }
 
   void updatePadStatus(bool active) {
-    final change = () {
+    final VoidCallback change = () {
       emoticonPadActive = active;
-      if (mounted) setState(() {});
+      if (mounted) {
+        setState(() {});
+      }
     };
     if (emoticonPadActive) {
       change();
     } else {
       if (MediaQuery.of(context).viewInsets.bottom != 0.0) {
-        SystemChannels.textInput.invokeMethod('TextInput.hide').whenComplete(
+        SystemChannels.textInput.invokeMethod<void>('TextInput.hide').whenComplete(
           () {
-            Future.delayed(300.milliseconds, null).whenComplete(change);
+            Future<void>.delayed(300.milliseconds, null).whenComplete(change);
           },
         );
       } else {
@@ -162,9 +158,9 @@ class ForwardPositionedState extends State<ForwardPositioned> {
   }
 
   void insertText(String text) {
-    final value = _forwardController.value;
-    final start = value.selection.baseOffset;
-    final end = value.selection.extentOffset;
+    final TextEditingValue value = _forwardController.value;
+    final int start = value.selection.baseOffset;
+    final int end = value.selection.extentOffset;
     if (value.selection.isValid) {
       String newText = '';
       if (value.selection.isCollapsed) {
@@ -185,7 +181,9 @@ class ForwardPositionedState extends State<ForwardPositioned> {
           extentOffset: end + text.length,
         ),
       );
-      if (mounted) setState(() {});
+      if (mounted) {
+        setState(() {});
+      }
     }
   }
 
@@ -196,14 +194,16 @@ class ForwardPositionedState extends State<ForwardPositioned> {
         controller: _forwardController,
       );
 
-  void mentionPeople(context) {
+  void mentionPeople(BuildContext context) {
     showDialog<User>(
       context: context,
       builder: (BuildContext context) => MentionPeopleDialog(),
-    ).then((user) {
-      if (_focusNode.canRequestFocus) _focusNode.requestFocus();
+    ).then((dynamic user) {
+      if (_focusNode.canRequestFocus) {
+        _focusNode.requestFocus();
+      }
       if (user != null) {
-        Future.delayed(250.milliseconds, () {
+        Future<void>.delayed(250.milliseconds, () {
           insertText('<M ${user.id}>@${user.nickname}<\/M>');
         });
       }
@@ -217,9 +217,9 @@ class ForwardPositionedState extends State<ForwardPositioned> {
             RoundedCheckbox(
               activeColor: currentThemeColor,
               value: commentAtTheMeanTime,
-              onChanged: (value) {
+              onChanged: (dynamic value) {
                 setState(() {
-                  commentAtTheMeanTime = value;
+                  commentAtTheMeanTime = value as bool;
                 });
               },
               materialTapTargetSize: MaterialTapTargetSize.shrinkWrap,
@@ -230,7 +230,7 @@ class ForwardPositionedState extends State<ForwardPositioned> {
                 fontSize: suSetSp(20.0),
               ),
             ),
-            Spacer(),
+            const Spacer(),
 //            GestureDetector(
 //              behavior: HitTestBehavior.opaque,
 //              onTap: _addImage,
@@ -277,38 +277,39 @@ class ForwardPositionedState extends State<ForwardPositioned> {
                 ),
               ),
             ),
-            !_forwarding
-                ? GestureDetector(
-                    behavior: HitTestBehavior.opaque,
-                    child: Padding(
-                      padding: EdgeInsets.symmetric(
-                        horizontal: suSetWidth(6.0),
-                      ),
-                      child: Icon(
-                        Icons.send,
-                        size: suSetWidth(32.0),
-                        color: currentThemeColor,
-                      ),
-                    ),
-                    onTap: () => _request(context),
-                  )
-                : Padding(
-                    padding: EdgeInsets.symmetric(
-                      horizontal: suSetWidth(14.0),
-                    ),
-                    child: SizedBox(
-                      width: suSetWidth(12.0),
-                      height: suSetWidth(12.0),
-                      child: PlatformProgressIndicator(strokeWidth: 2.0),
-                    ),
+            if (!_forwarding)
+              GestureDetector(
+                behavior: HitTestBehavior.opaque,
+                child: Padding(
+                  padding: EdgeInsets.symmetric(
+                    horizontal: suSetWidth(6.0),
+                  ),
+                  child: Icon(
+                    Icons.send,
+                    size: suSetWidth(32.0),
+                    color: currentThemeColor,
                   ),
+                ),
+                onTap: () => _request(context),
+              )
+            else
+              Padding(
+                padding: EdgeInsets.symmetric(
+                  horizontal: suSetWidth(14.0),
+                ),
+                child: SizedBox(
+                  width: suSetWidth(12.0),
+                  height: suSetWidth(12.0),
+                  child: const PlatformProgressIndicator(strokeWidth: 2.0),
+                ),
+              ),
           ],
         ),
       );
 
   @override
   Widget build(BuildContext context) {
-    final keyboardHeight = MediaQuery.of(context).viewInsets.bottom;
+    final double keyboardHeight = MediaQuery.of(context).viewInsets.bottom;
     if (keyboardHeight > 0) {
       emoticonPadActive = false;
     }
diff --git a/lib/widgets/dialogs/loading_dialog.dart b/lib/widgets/dialogs/loading_dialog.dart
index dc3c10d9..086dee85 100755
--- a/lib/widgets/dialogs/loading_dialog.dart
+++ b/lib/widgets/dialogs/loading_dialog.dart
@@ -5,10 +5,6 @@ import 'package:flutter/material.dart';
 import 'package:openjmu/constants/constants.dart';
 
 class LoadingDialog extends StatefulWidget {
-  final LoadingDialogController controller;
-  final String text;
-  final bool isGlobal;
-
   const LoadingDialog({
     Key key,
     this.text,
@@ -16,16 +12,20 @@ class LoadingDialog extends StatefulWidget {
     this.isGlobal = false,
   }) : super(key: key);
 
+  final LoadingDialogController controller;
+  final String text;
+  final bool isGlobal;
+
   @override
   State<StatefulWidget> createState() => LoadingDialogState();
 
   static void show(
-    context, {
+    BuildContext context, {
     LoadingDialogController controller,
     String text,
     bool isGlobal,
   }) {
-    showDialog<Null>(
+    showDialog<void>(
       context: context,
       builder: (_) => LoadingDialog(
         controller: controller,
@@ -40,14 +40,16 @@ class LoadingDialogState extends State<LoadingDialog> {
   Duration duration = 1500.milliseconds;
   String type, text;
   VoidCallback customPop;
-  Widget icon = SpinKitWidget();
+  Widget icon = const SpinKitWidget();
 
   @override
   void initState() {
     super.initState();
     widget.controller?.dialogState = this;
-    this.text = widget.text;
-    if (mounted) setState(() {});
+    text = widget.text;
+    if (mounted) {
+      setState(() {});
+    }
   }
 
   @override
@@ -57,7 +59,7 @@ class LoadingDialogState extends State<LoadingDialog> {
   }
 
   @override
-  void didUpdateWidget(oldWidget) {
+  void didUpdateWidget(LoadingDialog oldWidget) {
     super.didUpdateWidget(oldWidget);
     widget.controller?.dialogState = this;
   }
@@ -72,26 +74,36 @@ class LoadingDialogState extends State<LoadingDialog> {
     this.type = type;
     this.icon = icon;
     this.text = text;
-    if (duration != null) this.duration = duration;
-    if (customPop != null) this.customPop = customPop;
-    if (mounted) setState(() {});
+    if (duration != null) {
+      duration = duration;
+    }
+    if (customPop != null) {
+      customPop = customPop;
+    }
+    if (mounted) {
+      setState(() {});
+    }
   }
 
   void updateIcon(Widget icon) {
     this.icon = icon;
-    if (mounted) setState(() {});
+    if (mounted) {
+      setState(() {});
+    }
   }
 
   void updateText(String text) {
     this.text = text;
-    if (mounted) setState(() {});
+    if (mounted) {
+      setState(() {});
+    }
   }
 
   @override
   Widget build(BuildContext context) {
     if (!(widget.isGlobal ?? false)) {
-      if (this.type != null && this.type != 'loading') {
-        Future.delayed(duration, () {
+      if (type != null && type != 'loading') {
+        Future<void>.delayed(duration, () {
           try {
             if (customPop != null) {
               customPop();
@@ -102,7 +114,7 @@ class LoadingDialogState extends State<LoadingDialog> {
             debugPrint('Error when running pop in loading dialog: $e');
           }
         });
-      } else if (this.type == 'dismiss') {
+      } else if (type == 'dismiss') {
         try {
           if (customPop != null) {
             customPop();
@@ -158,15 +170,15 @@ class LoadingDialogState extends State<LoadingDialog> {
 class LoadingDialogController {
   LoadingDialogState dialogState;
 
-  void updateText(text) {
+  void updateText(String text) {
     dialogState.updateText(text);
   }
 
-  void updateIcon(icon) {
+  void updateIcon(Widget icon) {
     dialogState.updateIcon(icon);
   }
 
-  void updateContent(type, icon, text, duration) {
+  void updateContent(String type, Widget icon, String text, Duration duration) {
     dialogState.updateContent(type: type, icon: icon, text: text, duration: duration);
   }
 
@@ -190,7 +202,7 @@ class LoadingDialogController {
         dialogState.updateContent(
           type: 'failed',
           icon: RotationTransition(
-            turns: AlwaysStoppedAnimation(45 / 360),
+            turns: const AlwaysStoppedAnimation<double>(45 / 360),
             child: Icon(Icons.add_circle, color: Colors.redAccent, size: suSetWidth(60.0)),
           ),
           text: text,
@@ -200,7 +212,7 @@ class LoadingDialogController {
       case 'loading':
         dialogState.updateContent(
           type: 'loading',
-          icon: CircularProgressIndicator(),
+          icon: const CircularProgressIndicator(),
           text: text,
           duration: duration,
         );
@@ -208,7 +220,7 @@ class LoadingDialogController {
       case 'dismiss':
         dialogState.updateContent(
           type: 'dismiss',
-          icon: CircularProgressIndicator(),
+          icon: const CircularProgressIndicator(),
           text: text,
           duration: duration,
         );
diff --git a/lib/widgets/dialogs/manually_set_sid_dialog.dart b/lib/widgets/dialogs/manually_set_sid_dialog.dart
index 27bb8ae8..d9becc76 100644
--- a/lib/widgets/dialogs/manually_set_sid_dialog.dart
+++ b/lib/widgets/dialogs/manually_set_sid_dialog.dart
@@ -30,11 +30,11 @@ class _ManuallySetSidDialogState extends State<ManuallySetSidDialog> {
       });
   }
 
-  void updateSid(context) {
+  void updateSid(BuildContext context) {
     UserAPI.currentUser.sid = sid;
     UserAPI.currentUser.ticket = sid;
     Navigator.of(context).pop();
-    debugPrint("${UserAPI.currentUser}");
+    debugPrint('${UserAPI.currentUser}');
   }
 
   @override
@@ -57,7 +57,7 @@ class _ManuallySetSidDialogState extends State<ManuallySetSidDialog> {
                 children: <Widget>[
                   Center(
                     child: Text(
-                      "Set SID Manually (DEBUG)",
+                      'Set SID Manually (DEBUG)',
                       style: Theme.of(context).textTheme.title,
                     ),
                   ),
@@ -81,9 +81,7 @@ class _ManuallySetSidDialogState extends State<ManuallySetSidDialog> {
                           borderSide: BorderSide(color: Colors.grey[850]),
                         ),
                         hintText: currentUser.signature,
-                        hintStyle: TextStyle(
-                          textBaseline: TextBaseline.alphabetic,
-                        ),
+                        hintStyle: const TextStyle(textBaseline: TextBaseline.alphabetic),
                       ),
                       cursorColor: currentThemeColor,
                     ),
@@ -96,7 +94,7 @@ class _ManuallySetSidDialogState extends State<ManuallySetSidDialog> {
                           child: CupertinoDialogAction(
                             isDefaultAction: true,
                             child: Text(
-                              "取消",
+                              '取消',
                               style: TextStyle(fontSize: suSetSp(18.0)),
                             ),
                             onPressed: () => Navigator.of(context).pop(),
@@ -105,7 +103,7 @@ class _ManuallySetSidDialogState extends State<ManuallySetSidDialog> {
                         Expanded(
                           child: CupertinoDialogAction(
                             child: Text(
-                              "保存",
+                              '保存',
                               style: TextStyle(
                                 color:
                                     canSave ? currentThemeColor : Theme.of(context).disabledColor,
diff --git a/lib/widgets/dialogs/mention_people_dialog.dart b/lib/widgets/dialogs/mention_people_dialog.dart
index fbfa1977..b1e12fe1 100755
--- a/lib/widgets/dialogs/mention_people_dialog.dart
+++ b/lib/widgets/dialogs/mention_people_dialog.dart
@@ -8,9 +8,9 @@ class MentionPeopleDialog extends StatefulWidget {
 }
 
 class EditSignatureDialogState extends State<MentionPeopleDialog> {
-  final _textEditingController = TextEditingController();
+  final TextEditingController _textEditingController = TextEditingController();
   String query = '';
-  List<User> users = [];
+  final List<User> users = <User>[];
 
   bool loading = false;
 
@@ -18,7 +18,9 @@ class EditSignatureDialogState extends State<MentionPeopleDialog> {
   void initState() {
     _textEditingController.addListener(() {
       query = _textEditingController.text;
-      if (mounted) setState(() {});
+      if (mounted) {
+        setState(() {});
+      }
     });
     super.initState();
   }
@@ -31,19 +33,25 @@ class EditSignatureDialogState extends State<MentionPeopleDialog> {
 
   void requestSearch() {
     if (query.isEmpty || loading) {
-      if (query.isEmpty) showToast('要搜的人难道不配有名字吗？🤔');
+      if (query.isEmpty) {
+        showToast('要搜的人难道不配有名字吗？🤔');
+      }
     } else {
       loading = true;
-      if (mounted) setState(() {});
-      UserAPI.searchUser(query).then((response) {
+      if (mounted) {
+        setState(() {});
+      }
+      UserAPI.searchUser(query).then((dynamic response) {
         users.clear();
-        response['data'].forEach((userData) {
-          users.add(User.fromJson(userData));
+        response['data'].forEach((dynamic userData) {
+          users.add(User.fromJson(userData as Map<String, dynamic>));
         });
         loading = false;
-        if (mounted) setState(() {});
-      }).catchError((e) {
-        debugPrint(e.toString());
+        if (mounted) {
+          setState(() {});
+        }
+      }).catchError((dynamic e) {
+        debugPrint('Failed when request search: $e');
         loading = false;
       });
     }
@@ -51,10 +59,8 @@ class EditSignatureDialogState extends State<MentionPeopleDialog> {
 
   Widget get title => Center(
         child: Text(
-          "提到用户",
-          style: Theme.of(context).textTheme.title.copyWith(
-                fontSize: suSetSp(24.0),
-              ),
+          '提到用户',
+          style: Theme.of(context).textTheme.title.copyWith(fontSize: suSetSp(24.0)),
         ),
       );
 
@@ -66,8 +72,8 @@ class EditSignatureDialogState extends State<MentionPeopleDialog> {
           decoration: InputDecoration(
             border: InputBorder.none,
             contentPadding: EdgeInsets.zero,
-            hintText: "请输入名字进行搜索",
-            hintStyle: TextStyle(textBaseline: TextBaseline.alphabetic),
+            hintText: '请输入名字进行搜索',
+            hintStyle: const TextStyle(textBaseline: TextBaseline.alphabetic),
           ),
           textInputAction: TextInputAction.search,
           style: Theme.of(context).textTheme.body1.copyWith(
@@ -77,7 +83,9 @@ class EditSignatureDialogState extends State<MentionPeopleDialog> {
           scrollPadding: EdgeInsets.zero,
           maxLines: 1,
           onChanged: (String value) {
-            if (value.length + 1 == 30) return null;
+            if (value.length + 1 == 30) {
+              return null;
+            }
           },
           onSubmitted: (_) => requestSearch(),
         ),
@@ -97,7 +105,7 @@ class EditSignatureDialogState extends State<MentionPeopleDialog> {
         constraints: BoxConstraints(maxHeight: Screens.height / 3),
         child: SingleChildScrollView(
           child: Wrap(
-            children: List<Widget>.generate(users.length, (index) => user(index)),
+            children: List<Widget>.generate(users.length, (int index) => user(index)),
           ),
         ),
       );
@@ -163,12 +171,13 @@ class EditSignatureDialogState extends State<MentionPeopleDialog> {
                       child: Row(
                         children: <Widget>[
                           searchField,
-                          !loading
-                              ? searchButton
-                              : SizedBox.fromSize(
-                                  size: Size.square(suSetWidth(32.0)),
-                                  child: PlatformProgressIndicator(),
-                                ),
+                          if (!loading)
+                            searchButton
+                          else
+                            SizedBox.fromSize(
+                              size: Size.square(suSetWidth(32.0)),
+                              child: const PlatformProgressIndicator(),
+                            ),
                         ],
                       ),
                     ),
diff --git a/lib/widgets/image/image_crop_helper.dart b/lib/widgets/image/image_crop_helper.dart
index c4d3806a..af5c720c 100644
--- a/lib/widgets/image/image_crop_helper.dart
+++ b/lib/widgets/image/image_crop_helper.dart
@@ -1,62 +1,66 @@
 import 'dart:isolate';
+import 'dart:typed_data';
+import 'package:flutter/material.dart' hide Image;
 import "package:isolate/load_balancer.dart";
 import "package:isolate/isolate_runner.dart";
 import 'package:extended_image/extended_image.dart';
 import 'package:image/image.dart';
 import 'package:image_editor/image_editor.dart';
 
-final loadBalancer = LoadBalancer.create(1, IsolateRunner.spawn);
+final Future<LoadBalancer> loadBalancer = LoadBalancer.create(1, IsolateRunner.spawn);
 
 Future<dynamic> isolateDecodeImage(List<int> data) async {
-  final response = ReceivePort();
+  final ReceivePort response = ReceivePort();
   await Isolate.spawn(_isolateDecodeImage, response.sendPort);
-  final sendPort = await response.first;
-  final answer = ReceivePort();
-  sendPort.send([answer.sendPort, data]);
+  final SendPort sendPort = await response.first as SendPort;
+  final ReceivePort answer = ReceivePort();
+  sendPort.send(<dynamic>[answer.sendPort, data]);
   return answer.first;
 }
 
 void _isolateDecodeImage(SendPort port) {
-  final rPort = ReceivePort();
+  final ReceivePort rPort = ReceivePort();
   port.send(rPort.sendPort);
-  rPort.listen((message) {
-    final send = message[0] as SendPort;
-    final data = message[1] as List<int>;
+  rPort.listen((dynamic message) {
+    final SendPort send = message[0] as SendPort;
+    final List<int> data = message[1] as List<int>;
     send.send(decodeImage(data));
   });
 }
 
 Future<dynamic> isolateEncodeImage(Image src) async {
-  final response = ReceivePort();
+  final ReceivePort response = ReceivePort();
   await Isolate.spawn(_isolateEncodeImage, response.sendPort);
-  final sendPort = await response.first;
-  final answer = ReceivePort();
-  sendPort.send([answer.sendPort, src]);
+  final SendPort sendPort = await response.first as SendPort;
+  final ReceivePort answer = ReceivePort();
+  sendPort.send(<dynamic>[answer.sendPort, src]);
   return answer.first;
 }
 
 void _isolateEncodeImage(SendPort port) {
-  final rPort = ReceivePort();
+  final ReceivePort rPort = ReceivePort();
   port.send(rPort.sendPort);
-  rPort.listen((message) {
-    final send = message[0] as SendPort;
-    final src = message[1] as Image;
+  rPort.listen((dynamic message) {
+    final SendPort send = message[0] as SendPort;
+    final Image src = message[1] as Image;
     send.send(encodeJpg(src));
   });
 }
 
 Future<List<int>> cropImage({ExtendedImageEditorState state}) async {
-  final cropRect = state.getCropRect();
-  final action = state.editAction;
+  final Rect cropRect = state.getCropRect();
+  final EditActionDetails action = state.editAction;
 
-  final rotateAngle = action.rotateAngle.toInt();
-  final flipHorizontal = action.flipY;
-  final flipVertical = action.flipX;
-  final img = state.rawImageData;
+  final int rotateAngle = action.rotateAngle.toInt();
+  final bool flipHorizontal = action.flipY;
+  final bool flipVertical = action.flipX;
+  final Uint8List img = state.rawImageData;
 
-  ImageEditorOption option = ImageEditorOption();
+  final ImageEditorOption option = ImageEditorOption();
 
-  if (action.needCrop) option.addOption(ClipOption.fromRect(cropRect));
+  if (action.needCrop) {
+    option.addOption(ClipOption.fromRect(cropRect));
+  }
 
   if (action.needFlip) {
     option.addOption(FlipOption(horizontal: flipHorizontal, vertical: flipVertical));
@@ -66,7 +70,7 @@ Future<List<int>> cropImage({ExtendedImageEditorState state}) async {
     option.addOption(RotateOption(rotateAngle));
   }
 
-  final result = await ImageEditor.editImage(
+  final Uint8List result = await ImageEditor.editImage(
     image: img,
     imageEditorOption: option,
   );
diff --git a/lib/widgets/image/image_crop_page.dart b/lib/widgets/image/image_crop_page.dart
index 01eecac7..f1f9747d 100755
--- a/lib/widgets/image/image_crop_page.dart
+++ b/lib/widgets/image/image_crop_page.dart
@@ -21,15 +21,15 @@ class ImageCropPage extends StatefulWidget {
 }
 
 class _ImageCropPageState extends State<ImageCropPage> {
-  final _editorKey = GlobalKey<ExtendedImageEditorState>();
-  final _controller = LoadingDialogController();
+  final GlobalKey<ExtendedImageEditorState> _editorKey = GlobalKey<ExtendedImageEditorState>();
+  final LoadingDialogController _controller = LoadingDialogController();
   File _file;
   bool _cropping = false;
   bool firstLoad = true;
 
   @override
   void initState() {
-    _openImage().catchError((e) {});
+    _openImage().catchError((dynamic e) {});
     super.initState();
   }
 
@@ -39,10 +39,14 @@ class _ImageCropPageState extends State<ImageCropPage> {
     super.dispose();
   }
 
-  Future _openImage() async {
-    final file = await ImagePicker.pickImage(source: ImageSource.gallery);
-    if (file != null) _file = file;
-    if (mounted) setState(() {});
+  Future<void> _openImage() async {
+    final File file = await ImagePicker.pickImage(source: ImageSource.gallery);
+    if (file != null) {
+      _file = file;
+    }
+    if (mounted) {
+      setState(() {});
+    }
     resetCrop();
   }
 
@@ -58,8 +62,10 @@ class _ImageCropPageState extends State<ImageCropPage> {
     _editorKey.currentState?.rotate(right: right);
   }
 
-  void _cropImage(context) async {
-    if (_cropping) return;
+  Future<void> _cropImage(BuildContext context) async {
+    if (_cropping) {
+      return;
+    }
     LoadingDialog.show(
       context,
       text: '正在更新头像',
@@ -67,10 +73,10 @@ class _ImageCropPageState extends State<ImageCropPage> {
     );
     _cropping = true;
     try {
-      final path = (await getApplicationDocumentsDirectory()).path;
-      final file = File('$path/_temp_avatar.jpg');
+      final String path = (await getApplicationDocumentsDirectory()).path;
+      final File file = File('$path/_temp_avatar.jpg');
       file.writeAsBytesSync(await cropImage(state: _editorKey.currentState));
-      final compressedFile = await FlutterNativeImage.compressImage(
+      final File compressedFile = await FlutterNativeImage.compressImage(
         file.path,
         quality: 100,
         targetWidth: 640,
@@ -83,10 +89,10 @@ class _ImageCropPageState extends State<ImageCropPage> {
     }
   }
 
-  Future<void> uploadImage(context, file) async {
+  Future<void> uploadImage(BuildContext context, File file) async {
     try {
-      final formData = await createForm(file);
-      await NetUtils.postWithCookieSet(API.userAvatarUpload, data: formData);
+      final FormData formData = await createForm(file);
+      await NetUtils.postWithCookieSet<void>(API.userAvatarUpload, data: formData);
       _controller.changeState('success', '头像更新成功');
       _cropping = false;
       UserAPI.avatarLastModified = DateTime.now().millisecondsSinceEpoch;
@@ -100,8 +106,8 @@ class _ImageCropPageState extends State<ImageCropPage> {
     }
   }
 
-  Future createForm(File file) async {
-    return FormData.from({
+  Future<FormData> createForm(File file) async {
+    return FormData.from(<String, dynamic>{
       'offset': 0,
       'md5': md5.convert(await file.readAsBytes()),
       'photo': UploadFileInfo(file, path.basename(file.path)),
@@ -134,7 +140,7 @@ class _ImageCropPageState extends State<ImageCropPage> {
                     mode: ExtendedImageMode.editor,
                     enableLoadState: true,
                     extendedImageEditorKey: _editorKey,
-                    initEditorConfigHandler: (state) {
+                    initEditorConfigHandler: (ExtendedImageState state) {
                       return EditorConfig(
                         maxScale: 8.0,
                         cropRectPadding: const EdgeInsets.all(30.0),
@@ -165,7 +171,7 @@ class _ImageCropPageState extends State<ImageCropPage> {
                         ),
                       ),
                       highlightColor: Colors.red,
-                      customBorder: CircleBorder(),
+                      customBorder: const CircleBorder(),
                     ),
                   ),
           ),
diff --git a/lib/widgets/image/image_viewer.dart b/lib/widgets/image/image_viewer.dart
index 174e0f51..ab14df05 100755
--- a/lib/widgets/image/image_viewer.dart
+++ b/lib/widgets/image/image_viewer.dart
@@ -19,12 +19,6 @@ import 'package:openjmu/widgets/image/image_gesture_detector.dart';
   pageRouteType: PageRouteType.transparent,
 )
 class ImageViewer extends StatefulWidget {
-  final int index;
-  final List<ImageBean> pics;
-  final bool needsClear;
-  final Post post;
-  final String heroPrefix;
-
   const ImageViewer({
     @required this.index,
     @required this.pics,
@@ -33,19 +27,27 @@ class ImageViewer extends StatefulWidget {
     this.post,
   });
 
+  final int index;
+  final List<ImageBean> pics;
+  final bool needsClear;
+  final Post post;
+  final String heroPrefix;
+
   @override
   ImageViewerState createState() => ImageViewerState();
 }
 
 class ImageViewerState extends State<ImageViewer> with TickerProviderStateMixin {
-  final pageStreamController = StreamController<int>.broadcast();
-  final backgroundOpacityStreamController = StreamController<double>.broadcast();
-  final slidePageKey = GlobalKey<ExtendedImageSlidePageState>();
+  final StreamController<int> pageStreamController = StreamController<int>.broadcast();
+  final StreamController<double> backgroundOpacityStreamController =
+      StreamController<double>.broadcast();
+  final GlobalKey<ExtendedImageSlidePageState> slidePageKey =
+      GlobalKey<ExtendedImageSlidePageState>();
   int currentIndex;
   bool popping = false;
 
   AnimationController _doubleTapAnimationController;
-  Animation _doubleTapCurveAnimation;
+  Animation<double> _doubleTapCurveAnimation;
   Animation<double> _doubleTapAnimation;
   VoidCallback _doubleTapListener;
 
@@ -63,10 +65,7 @@ class ImageViewerState extends State<ImageViewer> with TickerProviderStateMixin
 
     _controller = PageController(initialPage: currentIndex);
 
-    _doubleTapAnimationController = AnimationController(
-      duration: const Duration(milliseconds: 200),
-      vsync: this,
-    );
+    _doubleTapAnimationController = AnimationController(duration: 200.milliseconds, vsync: this);
     _doubleTapCurveAnimation = CurvedAnimation(
       parent: _doubleTapAnimationController,
       curve: Curves.linear,
@@ -75,7 +74,7 @@ class ImageViewerState extends State<ImageViewer> with TickerProviderStateMixin
 
   @override
   void dispose() {
-    final provider = Provider.of<ThemesProvider>(currentContext, listen: false);
+    final ThemesProvider provider = Provider.of<ThemesProvider>(currentContext, listen: false);
     provider.setSystemUIDark(provider.dark);
     pageStreamController?.close();
     backgroundOpacityStreamController?.close();
@@ -85,12 +84,14 @@ class ImageViewerState extends State<ImageViewer> with TickerProviderStateMixin
   }
 
   void pop() {
-    if (popping) return;
+    if (popping) {
+      return;
+    }
     popping = true;
     backgroundOpacityStreamController.add(0.0);
   }
 
-  Future<void> _downloadImage(url, {AndroidDestinationType destination}) async {
+  Future<void> _downloadImage(String url, {AndroidDestinationType destination}) async {
     String path;
     try {
       String imageId;
@@ -100,21 +101,25 @@ class ImageViewerState extends State<ImageViewer> with TickerProviderStateMixin
               destination: AndroidDestinationType.custom(directory: 'OpenJMU'),
             )
           : imageId = await ImageDownloader.downloadImage(url);
-      if (imageId == null) return;
+      if (imageId == null) {
+        return;
+      }
       path = await ImageDownloader.findPath(imageId);
     } on PlatformException catch (error) {
       showCenterToast(error.message);
       return;
     }
-    if (!mounted) return;
+    if (!mounted) {
+      return;
+    }
     showCenterToast('图片保存至：$path');
     return;
   }
 
   void updateAnimation(ExtendedImageGestureState state) {
-    double begin = state.gestureDetails.totalScale;
-    double end = state.gestureDetails.totalScale == 1.0 ? 3.0 : 1.0;
-    Offset pointerDownPosition = state.pointerDownPosition;
+    final double begin = state.gestureDetails.totalScale;
+    final double end = state.gestureDetails.totalScale == 1.0 ? 3.0 : 1.0;
+    final Offset pointerDownPosition = state.pointerDownPosition;
 
     _doubleTapAnimation?.removeListener(_doubleTapListener);
     _doubleTapAnimationController
@@ -126,7 +131,7 @@ class ImageViewerState extends State<ImageViewer> with TickerProviderStateMixin
         doubleTapPosition: pointerDownPosition,
       );
     };
-    _doubleTapAnimation = Tween(
+    _doubleTapAnimation = Tween<double>(
       begin: begin,
       end: end,
     ).animate(_doubleTapCurveAnimation)
@@ -135,7 +140,7 @@ class ImageViewerState extends State<ImageViewer> with TickerProviderStateMixin
     _doubleTapAnimationController.forward();
   }
 
-  void onLongPress(context) {
+  void onLongPress(BuildContext context) {
     ConfirmationBottomSheet.show(
       context,
       children: <Widget>[
@@ -158,12 +163,14 @@ class ImageViewerState extends State<ImageViewer> with TickerProviderStateMixin
   }
 
   bool slideEndHandler(Offset offset) {
-    final shouldEnd = offset.distance > Offset(Screens.width, Screens.height).distance / 7;
-    if (shouldEnd) pop();
+    final bool shouldEnd = offset.distance > Offset(Screens.width, Screens.height).distance / 7;
+    if (shouldEnd) {
+      pop();
+    }
     return shouldEnd;
   }
 
-  Widget pageBuilder(context, index) {
+  Widget pageBuilder(BuildContext context, int index) {
     return ImageGestureDetector(
       context: context,
       imageViewerState: this,
@@ -181,7 +188,9 @@ class ImageViewerState extends State<ImageViewer> with TickerProviderStateMixin
         heroBuilderForSlidingPage: (Widget result) {
           if (index < widget.pics.length && widget.heroPrefix != null) {
             String tag = widget.heroPrefix;
-            if (widget.pics[index].postId != null) tag += '${widget.pics[index].postId}-';
+            if (widget.pics[index].postId != null) {
+              tag += '${widget.pics[index].postId}-';
+            }
             tag += '${widget.pics[index].id}';
 
             return Hero(
@@ -194,9 +203,9 @@ class ImageViewerState extends State<ImageViewer> with TickerProviderStateMixin
                 BuildContext fromHeroContext,
                 BuildContext toHeroContext,
               ) {
-                final Hero hero = flightDirection == HeroFlightDirection.pop
+                final Hero hero = (flightDirection == HeroFlightDirection.pop
                     ? fromHeroContext.widget
-                    : toHeroContext.widget;
+                    : toHeroContext.widget) as Hero;
                 return hero.child;
               },
             );
@@ -219,10 +228,10 @@ class ImageViewerState extends State<ImageViewer> with TickerProviderStateMixin
           Widget loader;
           switch (state.extendedImageLoadState) {
             case LoadState.loading:
-              loader = SpinKitWidget();
+              loader = const SpinKitWidget();
               break;
             case LoadState.completed:
-              // TODO: GIF will setState and cause this flash.
+              // TODO(AlexVincent525): GIF will setState and cause this flash.
 //              loader = FadeTransition(
 //                opacity: Tween(
 //                  begin: 0.0,
@@ -254,7 +263,7 @@ class ImageViewerState extends State<ImageViewer> with TickerProviderStateMixin
         slidePageBackgroundHandler: slidePageBackgroundHandler,
         slideEndHandler: slideEndHandler,
         resetPageDuration: widget.heroPrefix != null ? 300.milliseconds : 1.microseconds,
-        child: AnnotatedRegion(
+        child: AnnotatedRegion<SystemUiOverlayStyle>(
           value: SystemUiOverlayStyle.light,
           child: Material(
             type: MaterialType.transparency,
@@ -278,7 +287,7 @@ class ImageViewerState extends State<ImageViewer> with TickerProviderStateMixin
                   child: StreamBuilder<double>(
                     initialData: 1.0,
                     stream: backgroundOpacityStreamController.stream,
-                    builder: (context, data) => Opacity(
+                    builder: (BuildContext context, AsyncSnapshot<double> data) => Opacity(
                       opacity: popping ? 0.0 : data.data,
                       child: ViewAppBar(
                         post: widget.post,
@@ -295,7 +304,7 @@ class ImageViewerState extends State<ImageViewer> with TickerProviderStateMixin
                     child: StreamBuilder<double>(
                       initialData: 1.0,
                       stream: backgroundOpacityStreamController.stream,
-                      builder: (context, data) => Opacity(
+                      builder: (BuildContext context, AsyncSnapshot<double> data) => Opacity(
                         opacity: popping ? 0.0 : data.data,
                         child: ImageList(
                           controller: _controller,
@@ -316,18 +325,18 @@ class ImageViewerState extends State<ImageViewer> with TickerProviderStateMixin
 }
 
 class ImageList extends StatelessWidget {
-  final PageController controller;
-  final StreamController<int> pageStreamController;
-  final int index;
-  final List<ImageBean> pics;
-
-  ImageList({
+  const ImageList({
     this.controller,
     this.pageStreamController,
     this.index,
     this.pics,
   });
 
+  final PageController controller;
+  final StreamController<int> pageStreamController;
+  final int index;
+  final List<ImageBean> pics;
+
   @override
   Widget build(BuildContext context) {
     return Container(
@@ -345,13 +354,13 @@ class ImageList extends StatelessWidget {
       child: StreamBuilder<int>(
         initialData: index,
         stream: pageStreamController.stream,
-        builder: (context, data) => SizedBox(
+        builder: (BuildContext context, AsyncSnapshot<int> data) => SizedBox(
           height: suSetHeight(52.0),
           child: Row(
             mainAxisAlignment: MainAxisAlignment.center,
             children: List<Widget>.generate(
               pics.length,
-              (i) => Container(
+              (int i) => Container(
                 margin: EdgeInsets.symmetric(horizontal: suSetWidth(2.0)),
                 width: suSetWidth(52.0),
                 height: suSetWidth(52.0),
@@ -395,15 +404,15 @@ class ImageList extends StatelessWidget {
 }
 
 class ViewAppBar extends StatelessWidget {
-  final Post post;
-  final VoidCallback onMoreClicked;
-
   const ViewAppBar({
     Key key,
     this.post,
     this.onMoreClicked,
   }) : super(key: key);
 
+  final Post post;
+  final VoidCallback onMoreClicked;
+
   @override
   Widget build(BuildContext context) {
     return Material(
@@ -442,7 +451,7 @@ class ViewAppBar extends StatelessWidget {
                         ),
                       ],
                     )
-                  : SizedBox.shrink(),
+                  : const SizedBox.shrink(),
             ),
             if (onMoreClicked != null)
               IconButton(
@@ -458,19 +467,23 @@ class ViewAppBar extends StatelessWidget {
 }
 
 class ImageBean {
-  int id;
-  String imageUrl;
-  String imageThumbUrl;
-  int postId;
-
-  ImageBean({this.id, this.imageUrl, this.imageThumbUrl, this.postId});
+  const ImageBean({this.id, this.imageUrl, this.imageThumbUrl, this.postId});
+  final int id;
+  final String imageUrl;
+  final String imageThumbUrl;
+  final int postId;
 
   Map<String, dynamic> toJson() {
-    return {'id': id, 'imageUrl': imageUrl, 'imageThumbUrl': imageThumbUrl, 'postId': postId};
+    return <String, dynamic>{
+      'id': id,
+      'imageUrl': imageUrl,
+      'imageThumbUrl': imageThumbUrl,
+      'postId': postId,
+    };
   }
 
   @override
   String toString() {
-    return 'ImageBean ${JsonEncoder.withIndent('  ').convert(toJson())}';
+    return 'ImageBean ${const JsonEncoder.withIndent('  ').convert(toJson())}';
   }
 }
diff --git a/lib/widgets/messages/app_message_preview_widget.dart b/lib/widgets/messages/app_message_preview_widget.dart
index b13db059..0a63d6ea 100644
--- a/lib/widgets/messages/app_message_preview_widget.dart
+++ b/lib/widgets/messages/app_message_preview_widget.dart
@@ -12,9 +12,6 @@ import 'package:openjmu/constants/constants.dart';
 import 'package:openjmu/widgets/webapp_icon.dart';
 
 class AppMessagePreviewWidget extends StatefulWidget {
-  final AppMessage message;
-  final double height;
-
   const AppMessagePreviewWidget({
     @required this.message,
     this.height = 70.0,
@@ -22,6 +19,9 @@ class AppMessagePreviewWidget extends StatefulWidget {
   })  : assert(message != null),
         super(key: key);
 
+  final AppMessage message;
+  final double height;
+
   @override
   _AppMessagePreviewWidgetState createState() => _AppMessagePreviewWidgetState();
 }
@@ -49,8 +49,8 @@ class _AppMessagePreviewWidgetState extends State<AppMessagePreviewWidget>
     super.dispose();
   }
 
-  void timeFormat(_, {bool fromBuild = false}) {
-    final now = DateTime.now();
+  void timeFormat(Timer _, {bool fromBuild = false}) {
+    final DateTime now = DateTime.now();
     if (widget.message.sendTime.day == now.day &&
         widget.message.sendTime.month == now.month &&
         widget.message.sendTime.year == now.year) {
@@ -60,14 +60,21 @@ class _AppMessagePreviewWidgetState extends State<AppMessagePreviewWidget>
     } else {
       formattedTime = DateFormat('yy-MM-dd HH:mm').format(widget.message.sendTime);
     }
-    if (mounted && !fromBuild) setState(() {});
+    if (mounted && !fromBuild) {
+      setState(() {});
+    }
   }
 
   Widget get unreadCounter => Consumer<MessagesProvider>(
-        builder: (_, provider, __) {
-          final messages = provider.appsMessages[widget.message.appId];
-          final unreadMessages = messages.where((message) => !message.read)?.toList();
-          if (unreadMessages.isEmpty) return SizedBox.shrink();
+        builder: (_, MessagesProvider provider, __) {
+          final List<dynamic> messages = provider.appsMessages[widget.message.appId];
+          final List<AppMessage> unreadMessages = messages
+              .where((dynamic message) => !(message as AppMessage).read)
+              ?.toList()
+              ?.cast<AppMessage>();
+          if (unreadMessages.isEmpty) {
+            return const SizedBox.shrink();
+          }
           return Container(
             width: suSetWidth(28.0),
             height: suSetWidth(28.0),
@@ -77,8 +84,8 @@ class _AppMessagePreviewWidgetState extends State<AppMessagePreviewWidget>
             ),
             child: Center(
               child: Selector<ThemesProvider, bool>(
-                selector: (_, provider) => provider.dark,
-                builder: (_, dark, __) {
+                selector: (_, ThemesProvider provider) => provider.dark,
+                builder: (_, bool dark, __) {
                   return Text(
                     '${unreadMessages.length}',
                     style: TextStyle(
@@ -95,21 +102,27 @@ class _AppMessagePreviewWidgetState extends State<AppMessagePreviewWidget>
       );
 
   void updateApp() {
-    final provider = Provider.of<WebAppsProvider>(currentContext, listen: false);
-    app = provider.allApps.where((app) => app.appId == widget.message.appId).elementAt(0);
+    final WebAppsProvider provider = Provider.of<WebAppsProvider>(currentContext, listen: false);
+    app = provider.allApps
+        .where((dynamic app) => (app as WebApp).appId == widget.message.appId)
+        .elementAt(0);
   }
 
   void tryDecodeContent() {
     try {
-      final content = jsonDecode(widget.message.content);
-      widget.message.content = content['content'];
+      final Map<String, dynamic> content =
+          jsonDecode(widget.message.content) as Map<String, dynamic>;
+      widget.message.content = content['content'] as String;
       Provider.of<MessagesProvider>(currentContext, listen: false).saveAppsMessages();
-      if (mounted) setState(() {});
+      if (mounted) {
+        setState(() {});
+      }
     } catch (e) {
       return;
     }
   }
 
+  @override
   @mustCallSuper
   Widget build(BuildContext context) {
     super.build(context);
@@ -120,21 +133,23 @@ class _AppMessagePreviewWidgetState extends State<AppMessagePreviewWidget>
     return GestureDetector(
       behavior: HitTestBehavior.opaque,
       onTap: () {
-        navigatorState.pushNamed(Routes.OPENJMU_CHAT_APP_MESSAGE_PAGE, arguments: {'app': app});
+        navigatorState.pushNamed(
+          Routes.OPENJMU_CHAT_APP_MESSAGE_PAGE,
+          arguments: <String, dynamic>{'app': app},
+        );
       },
       child: Container(
-        padding: EdgeInsets.symmetric(horizontal: suSetSp(16.0)),
+        padding: EdgeInsets.symmetric(horizontal: suSetWidth(16.0)),
         height: suSetHeight(widget.height),
-        decoration: BoxDecoration(),
         child: Row(
           children: <Widget>[
             Padding(
-              padding: EdgeInsets.only(right: suSetSp(16.0)),
+              padding: EdgeInsets.only(right: suSetWidth(16.0)),
               child: WebAppIcon(app: app),
             ),
             Expanded(
               child: SizedBox(
-                height: suSetSp(60.0),
+                height: suSetHeight(60.0),
                 child: Column(
                   mainAxisAlignment: MainAxisAlignment.spaceBetween,
                   crossAxisAlignment: CrossAxisAlignment.start,
@@ -142,7 +157,7 @@ class _AppMessagePreviewWidgetState extends State<AppMessagePreviewWidget>
                     Row(
                       children: <Widget>[
                         SizedBox(
-                          height: suSetSp(30.0),
+                          height: suSetHeight(30.0),
                           child: app != null
                               ? Text(
                                   '${app.name ?? app.appId}',
@@ -151,7 +166,7 @@ class _AppMessagePreviewWidgetState extends State<AppMessagePreviewWidget>
                                         fontWeight: FontWeight.w500,
                                       ),
                                 )
-                              : SizedBox.shrink(),
+                              : const SizedBox.shrink(),
                         ),
                         Text(
                           ' $formattedTime',
@@ -159,7 +174,7 @@ class _AppMessagePreviewWidgetState extends State<AppMessagePreviewWidget>
                                 color: Theme.of(context).textTheme.body1.color.withOpacity(0.5),
                               ),
                         ),
-                        Spacer(),
+                        const Spacer(),
                         unreadCounter,
                       ],
                     ),
diff --git a/lib/widgets/messages/message_preview_widget.dart b/lib/widgets/messages/message_preview_widget.dart
index 9df8d369..72ff3991 100644
--- a/lib/widgets/messages/message_preview_widget.dart
+++ b/lib/widgets/messages/message_preview_widget.dart
@@ -10,20 +10,22 @@ import 'package:intl/intl.dart';
 import 'package:openjmu/constants/constants.dart';
 
 class MessagePreviewWidget extends StatefulWidget {
-  final int uid;
-  final WebApp app;
-  final Message message;
-  final List<Message> unreadMessages;
-
   const MessagePreviewWidget({
     this.uid,
     this.app,
     @required this.message,
     @required this.unreadMessages,
+    this.height = 80.0,
     Key key,
   })  : assert(uid != null || app != null),
         super(key: key);
 
+  final int uid;
+  final WebApp app;
+  final Message message;
+  final List<Message> unreadMessages;
+  final double height;
+
   @override
   _MessagePreviewWidgetState createState() => _MessagePreviewWidgetState();
 }
@@ -40,15 +42,17 @@ class _MessagePreviewWidgetState extends State<MessagePreviewWidget>
 
   @override
   void initState() {
-    UserAPI.getUserInfo(uid: widget.uid).then((response) {
-      user = UserInfo.fromJson(response.data);
-      if (mounted) setState(() {});
-    }).catchError((e) {
+    UserAPI.getUserInfo<void>(uid: widget.uid).then((dynamic response) {
+      user = UserInfo.fromJson((response as Response<dynamic>).data as Map<String, dynamic>);
+      if (mounted) {
+        setState(() {});
+      }
+    }).catchError((dynamic e) {
       debugPrint('$e');
     });
 
     timeFormat(null);
-    timeUpdateTimer = Timer.periodic(const Duration(minutes: 1), timeFormat);
+    timeUpdateTimer = Timer.periodic(1.minutes, timeFormat);
 
     super.initState();
   }
@@ -59,8 +63,8 @@ class _MessagePreviewWidgetState extends State<MessagePreviewWidget>
     super.dispose();
   }
 
-  void timeFormat(_) {
-    final now = DateTime.now();
+  void timeFormat(Timer _) {
+    final DateTime now = DateTime.now();
     if (widget.message.sendTime.day == now.day &&
         widget.message.sendTime.month == now.month &&
         widget.message.sendTime.year == now.year) {
@@ -70,24 +74,22 @@ class _MessagePreviewWidgetState extends State<MessagePreviewWidget>
     } else {
       formattedTime = DateFormat('yy-MM-dd HH:mm').format(widget.message.sendTime);
     }
-    if (mounted) setState(() {});
+    if (mounted) {
+      setState(() {});
+    }
   }
 
+  @override
   @mustCallSuper
   Widget build(BuildContext context) {
     super.build(context);
     return Container(
-      padding: EdgeInsets.symmetric(
-        horizontal: suSetSp(16.0),
-      ),
-      height: suSetSp(90.0),
-      decoration: BoxDecoration(),
+      padding: EdgeInsets.symmetric(horizontal: suSetWidth(16.0)),
+      height: suSetHeight(widget.height),
       child: Row(
         children: <Widget>[
           Padding(
-            padding: EdgeInsets.only(
-              right: suSetSp(16.0),
-            ),
+            padding: EdgeInsets.only(right: suSetWidth(16.0)),
             child: UserAPI.getAvatar(size: 60.0, uid: widget.uid),
           ),
           Expanded(
@@ -109,7 +111,7 @@ class _MessagePreviewWidgetState extends State<MessagePreviewWidget>
                                       fontWeight: FontWeight.w500,
                                     ),
                               )
-                            : SizedBox.shrink(),
+                            : const SizedBox.shrink(),
                       ),
                       Text(
                         ' $formattedTime',
@@ -117,7 +119,7 @@ class _MessagePreviewWidgetState extends State<MessagePreviewWidget>
                               color: Theme.of(context).textTheme.body1.color.withOpacity(0.5),
                             ),
                       ),
-                      Spacer(),
+                      const Spacer(),
                       Container(
                         width: suSetWidth(28.0),
                         height: suSetWidth(28.0),
diff --git a/lib/widgets/rounded_check_box.dart b/lib/widgets/rounded_check_box.dart
index 245f06c5..293c8ce2 100755
--- a/lib/widgets/rounded_check_box.dart
+++ b/lib/widgets/rounded_check_box.dart
@@ -255,7 +255,9 @@ class _RenderCheckbox extends RenderToggleable {
 
   @override
   set value(bool newValue) {
-    if (newValue == value) return;
+    if (newValue == value) {
+      return;
+    }
     _oldValue = value;
     super.value = newValue;
   }
@@ -342,7 +344,7 @@ class _RenderCheckbox extends RenderToggleable {
     final Canvas canvas = context.canvas;
     paintRadialReaction(canvas, offset, size.center(Offset.zero));
 
-    final Offset origin = offset + (size / 2.0 - const Size.square(_kEdgeSize) / 2.0);
+    final Offset origin = offset + (size / 2.0 - const Size.square(_kEdgeSize) / 2.0 as Offset);
     final AnimationStatus status = position.status;
     final double tNormalized =
         status == AnimationStatus.forward || status == AnimationStatus.completed
diff --git a/lib/widgets/webapp_icon.dart b/lib/widgets/webapp_icon.dart
index 4128f2b9..09c25f7a 100755
--- a/lib/widgets/webapp_icon.dart
+++ b/lib/widgets/webapp_icon.dart
@@ -6,18 +6,18 @@ import 'package:flutter_svg/flutter_svg.dart';
 import 'package:openjmu/constants/constants.dart';
 
 class WebAppIcon extends StatelessWidget {
-  final WebApp app;
-  final double size;
-
   const WebAppIcon({
     Key key,
     @required this.app,
     this.size = 60.0,
   }) : super(key: key);
 
+  final WebApp app;
+  final double size;
+
   Future<Widget> loadAsset() async {
     try {
-      final _ = await rootBundle.load(iconPath);
+      await rootBundle.load(iconPath);
       return SvgPicture.asset(iconPath, width: suSetWidth(size), height: suSetWidth(size));
     } catch (e) {
       debugPrint('Error when load webapp icon: $e.\nLoading fallback icon...');
@@ -39,14 +39,14 @@ class WebAppIcon extends StatelessWidget {
   @override
   Widget build(BuildContext context) {
     return Selector<SettingsProvider, bool>(
-      selector: (_, provider) => provider.newAppCenterIcon,
-      builder: (_, newAppCenterIcon, __) {
-        final shouldUseNew = !(currentUser?.isTeacher ?? false) || newAppCenterIcon;
+      selector: (_, SettingsProvider provider) => provider.newAppCenterIcon,
+      builder: (_, bool newAppCenterIcon, __) {
+        final bool shouldUseNew = !(currentUser?.isTeacher ?? false) || newAppCenterIcon;
         return shouldUseNew
-            ? FutureBuilder(
-                initialData: SizedBox.shrink(),
+            ? FutureBuilder<Widget>(
+                initialData: const SizedBox.shrink(),
                 future: loadAsset(),
-                builder: (_, snapshot) => SizedBox.fromSize(
+                builder: (_, AsyncSnapshot<Widget> snapshot) => SizedBox.fromSize(
                   size: Size.square(suSetWidth(size)),
                   child: Center(child: snapshot.data),
                 ),
diff --git a/lib/widgets/webview/in_app_webview.dart b/lib/widgets/webview/in_app_webview.dart
index e47cb2db..a4de81da 100755
--- a/lib/widgets/webview/in_app_webview.dart
+++ b/lib/widgets/webview/in_app_webview.dart
@@ -23,15 +23,6 @@ import 'package:openjmu/constants/constants.dart';
   ],
 )
 class InAppBrowserPage extends StatefulWidget {
-  final String url;
-  final String title;
-  final WebApp app;
-  final bool withCookie;
-  final bool withAppBar;
-  final bool withAction;
-  final bool withScaffold;
-  final bool keepAlive;
-
   const InAppBrowserPage({
     Key key,
     @required this.url,
@@ -44,6 +35,15 @@ class InAppBrowserPage extends StatefulWidget {
     this.keepAlive = false,
   }) : super(key: key);
 
+  final String url;
+  final String title;
+  final WebApp app;
+  final bool withCookie;
+  final bool withAppBar;
+  final bool withAction;
+  final bool withScaffold;
+  final bool keepAlive;
+
   @override
   _InAppBrowserPageState createState() => _InAppBrowserPageState();
 }
@@ -67,15 +67,17 @@ class _InAppBrowserPageState extends State<InAppBrowserPage> with AutomaticKeepA
     }
 
     Instances.eventBus
-      ..on<CourseScheduleRefreshEvent>().listen((event) {
-        if (mounted) loadCourseSchedule();
+      ..on<CourseScheduleRefreshEvent>().listen((CourseScheduleRefreshEvent event) {
+        if (mounted) {
+          loadCourseSchedule();
+        }
       });
     super.initState();
   }
 
   @override
   void dispose() {
-    SystemChannels.textInput.invokeMethod('TextInput.hide');
+    SystemChannels.textInput.invokeMethod<void>('TextInput.hide');
     super.dispose();
   }
 
@@ -87,21 +89,21 @@ class _InAppBrowserPageState extends State<InAppBrowserPage> with AutomaticKeepA
             '&night=${currentIsDark ? 1 : 0}',
       );
     } catch (e) {
-      debugPrint("$e");
+      debugPrint('$e');
     }
   }
 
   bool checkSchemeLoad(InAppWebViewController controller, String url) {
-    final protocolRegExp = RegExp(r'(http|https):\/\/([\w.]+\/?)\S*');
+    final RegExp protocolRegExp = RegExp(r'(http|https):\/\/([\w.]+\/?)\S*');
     if (!url.startsWith(protocolRegExp) && url.contains('://')) {
       debugPrint('Found scheme when load: $url');
       if (Platform.isAndroid) {
-        Future.delayed(1.microseconds, () async {
+        Future<void>.delayed(1.microseconds, () async {
           unawaited(controller.stopLoading());
           debugPrint('Try to launch intent...');
-          final appName = await ChannelUtils.getSchemeLaunchAppName(url);
+          final String appName = await ChannelUtils.getSchemeLaunchAppName(url);
           if (appName != null) {
-            final shouldLaunch = await waitForConfirmation(appName);
+            final bool shouldLaunch = await waitForConfirmation(appName);
             if (shouldLaunch) {
               await _launchURL(url: url);
             }
@@ -123,7 +125,7 @@ class _InAppBrowserPageState extends State<InAppBrowserPage> with AutomaticKeepA
         child: Text.rich(
           TextSpan(
             children: <InlineSpan>[
-              TextSpan(text: '即将打开应用\n'),
+              const TextSpan(text: '即将打开应用\n'),
               TextSpan(
                 text: '$applicationLabel',
                 style: TextStyle(fontSize: suSetSp(20.0), fontWeight: FontWeight.bold),
@@ -189,8 +191,8 @@ class _InAppBrowserPageState extends State<InAppBrowserPage> with AutomaticKeepA
     );
   }
 
-  void showMore(context) {
-    showModalBottomSheet(
+  void showMore(BuildContext context) {
+    showModalBottomSheet<void>(
       shape: RoundedRectangleBorder(
         borderRadius: BorderRadius.only(
           topLeft: Radius.circular(suSetWidth(20.0)),
@@ -242,16 +244,16 @@ class _InAppBrowserPageState extends State<InAppBrowserPage> with AutomaticKeepA
     );
   }
 
-  Future<Null> _launchURL({String url, bool forceSafariVC = true}) async {
-    final uri = Uri.encodeFull(url ?? this.url);
+  Future<void> _launchURL({String url, bool forceSafariVC = true}) async {
+    final String uri = Uri.encodeFull(url ?? this.url);
     if (await canLaunch(uri)) {
-      await launch(uri, forceSafariVC: Platform.isIOS ? forceSafariVC : false);
+      await launch(uri, forceSafariVC: Platform.isIOS && forceSafariVC);
     } else {
       showCenterErrorToast('无法打开网址: $uri');
     }
   }
 
-  Widget get appBar => PreferredSize(
+  PreferredSizeWidget get appBar => PreferredSize(
         preferredSize: Size.fromHeight(suSetHeight(kAppBarHeight)),
         child: Container(
           height: Screens.topSafeHeight + suSetHeight(kAppBarHeight),
@@ -291,7 +293,7 @@ class _InAppBrowserPageState extends State<InAppBrowserPage> with AutomaticKeepA
         ),
       );
 
-  Widget get refreshIndicator => Center(
+  Widget get refreshIndicator => const Center(
         child: Padding(
           padding: EdgeInsets.symmetric(horizontal: 16.0),
           child: SizedBox(
@@ -359,7 +361,7 @@ class _InAppBrowserPageState extends State<InAppBrowserPage> with AutomaticKeepA
             useOnDownloadStart: true,
             useShouldOverrideUrlLoading: true,
           ),
-          // TODO: Currently zoom control in android was broken, need to find the root cause.
+          // TODO(AlexVincent525): Currently zoom control in android was broken, need to find the root cause.
           android: AndroidInAppWebViewOptions(
             allowFileAccessFromFileURLs: true,
             allowUniversalAccessFromFileURLs: true,
@@ -400,19 +402,21 @@ class _InAppBrowserPageState extends State<InAppBrowserPage> with AutomaticKeepA
           _webViewController = controller;
 
           this.url = url;
-          final _title = (await controller.getTitle())?.trim();
+          final String _title = (await controller.getTitle())?.trim();
           if (_title != null && _title.isNotEmpty && _title != this.url) {
             title = _title;
           } else {
-            final ogTitle = await controller.evaluateJavascript(
+            final String ogTitle = await controller.evaluateJavascript(
               source: 'var ogTitle = document.querySelector(\'[property="og:title"]\');\n'
                   'if (ogTitle != undefined) ogTitle.content;',
-            );
+            ) as String;
             if (ogTitle != null) {
               title = ogTitle;
             }
           }
-          if (this.mounted) setState(() {});
+          if (mounted) {
+            setState(() {});
+          }
         },
         onConsoleMessage: (InAppWebViewController controller, ConsoleMessage consoleMessage) {
           _webViewController = controller;
@@ -425,7 +429,7 @@ class _InAppBrowserPageState extends State<InAppBrowserPage> with AutomaticKeepA
         onDownloadStart: (InAppWebViewController controller, String url) {
           _webViewController = controller;
 
-          debugPrint("WebView started download from: $url");
+          debugPrint('WebView started download from: $url');
           NetUtils.download(url);
         },
         onWebViewCreated: (InAppWebViewController controller) {