wip; nav: Disable bottom sheet dragging when scrolled

Signed-off-by: Zixuan James Li <zixuan@zulip.com>

lib/widgets/home.dart

@@ -89,7 +89,28 @@ class _HomePageState extends State<HomePage> {
   }
 }
 
-void showMenu(BuildContext context) {
+const Duration _bottomSheetEnterDuration = Duration(milliseconds: 250);
+const Duration _bottomSheetExitDuration = Duration(milliseconds: 200);
+
+class _PausableAnimationController extends AnimationController {
+  _PausableAnimationController({
+    required super.vsync,
+    super.duration,
+    super.reverseDuration,
+  });
+
+  bool paused = false;
+
+  @override
+  set value(double newValue) {
+    if (paused) {
+      return;
+    }
+    super.value = (newValue);
+  }
+}
+
+void showMenu(BuildContext context) async {
   final store = PerAccountStoreWidget.of(context);
   final designVariables = DesignVariables.of(context);
   final menuItems = <Widget>[
@@ -127,8 +148,16 @@ void showMenu(BuildContext context) {
     const SizedBox(height: 8),
     const _VersionInfo(),
   ];
-
-  showModalBottomSheet<void>(
+  final animationController = _PausableAnimationController(
+    vsync: Navigator.of(context),
+    duration: _bottomSheetEnterDuration,
+    reverseDuration: _bottomSheetExitDuration,
+  );
+  bool handleScroll(ScrollNotification notification) {
+    animationController.paused = notification.metrics.extentBefore != 0;
+    return false;
+  }
+  await showModalBottomSheet<void>(
     context: context,
     // Clip.hardEdge looks bad; Clip.antiAliasWithSaveLayer looks pixel-perfect
     // on my iPhone 13 Pro but is marked as "much slower":
@@ -137,6 +166,7 @@ void showMenu(BuildContext context) {
     useSafeArea: true,
     isScrollControlled: true,
     backgroundColor: designVariables.bgBotBar,
+    transitionAnimationController: animationController,
     builder: (BuildContext _) {
       return SafeArea(
         minimum: const EdgeInsets.only(bottom: 8),
@@ -148,18 +178,24 @@ void showMenu(BuildContext context) {
             Expanded(child: InsetShadowBox(
               top: 8, bottom: 8,
               color: designVariables.bgBotBar,
-              child: SingleChildScrollView(
-                padding: const EdgeInsets.symmetric(vertical: 8, horizontal: 8),
-                child: Column(
-                  mainAxisAlignment: MainAxisAlignment.start,
-                  children: menuItems)))),
+              child: NotificationListener<ScrollNotification>(
+                onNotification: handleScroll,
+                child: SingleChildScrollView(
+                  padding: const EdgeInsets.symmetric(vertical: 8, horizontal: 8),
+                  child: Column(
+                    mainAxisAlignment: MainAxisAlignment.start,
+                    children: menuItems))))),
             const Padding(
               padding: EdgeInsets.symmetric(horizontal: 16),
               child: Scaled(
                 scaleEnd: 0.95,
                 duration: Duration(milliseconds: 100),
                 child: SizedBox(height: 44, child: ActionSheetCancelButton()))),
           ]));
+    }).whenComplete(() {
+      // See [TransitionRoute.didPop].
+      animationController.paused = false;
+      animationController.reverse().whenComplete(() => animationController.dispose());
     });
 }