2021年开发笔记第一期

iOS13之后怎么获取Key Window

static var keyWindow:UIWindow? {
    if #available(iOS 13.0, *) {
        return UIApplication.shared.connectedScenes
            .filter({$0.activationState == .foregroundActive})
            .compactMap({$0 as? UIWindowScene})
            .first?.windows
            .filter({$0.isKeyWindow})
            .first
    } else {
        return UIApplication.shared.windows
            .filter({$0.isKeyWindow})
            .first
    }
}

'xxx_App' is annotated with @main and must provide a main static function of type () -> Void or () throws -> Void. Inheritance from non-protocol type 'App'

谷歌了半天，很多人都遇到过，但是都不能解决我的问题，后来研究发现，我项目存在一样的App名字的Struct，带上模块名字就修复了。

@main
struct Win_App: SwiftUI.App {
    ...
}

SwiftUI 怎么在任何 Function 中实行跳转

struct ContentView: View {
  	/// 控制何时进行跳转
    @State var action: Bool = false
    var body: some View {
        NavigationView {
            HStack(spacing:0) {
            		/// NavigationLink 返回 `EmptyView` 不污染界面
                NavigationLink(destination: destination, isActive: $action) {
                    EmptyView()
                }
                Text("Click me!")
                    .onTapGesture {
                        self.clicked()
                    }
            }
        }
    }
    func clicked() {
        /// 执行跳转
        action = true
    }
}

隐藏返回按钮文本

let backButtonAppearance = UIBarButtonItemAppearance()
backButtonAppearance.normal.titleTextAttributes = [
    .font : UIFont.systemFont(ofSize: 0),
]
appearance.backButtonAppearance = backButtonAppearance

修改 SwiftUI 返回按钮的颜色

NavigationView {
	...
}
.accentColor(.black)

需要注意的是官方说accentColor已经要废弃了，Use the asset catalog's accent color or View.tint(_:) instead."

但是替换为 tint不起作用。

隐藏 SwiftUI 的 UITabbar

需要在需要隐藏界面进行设置

struct PalletBindBoxNumberPage: View {
    ...
    var body: some View {
        ...
        .onAppear {
            App.tabBar?.isHidden = true
        }
        .onDisappear {
            App.tabBar?.isHidden = false
        }
    }
}

struct App {
    static var keyWindow:UIWindow? {
        if #available(iOS 13.0, *) {
            return UIApplication.shared.connectedScenes
                .filter({$0.activationState == .foregroundActive})
                .compactMap({$0 as? UIWindowScene})
                .first?.windows
                .filter({$0.isKeyWindow})
                .first
        } else {
            return UIApplication.shared.windows
                .filter({$0.isKeyWindow})
                .first
        }
    }
    
    static var tabBar:UITabBar? {
        return keyWindow?.rootViewController
            .flatMap({$0.view})
            .flatMap({$0.subviews.first})
            .flatMap({$0.subviews.first})
            .map({$0.subviews})
            .map({$0.compactMap({$0 as? UITabBar})})
            .flatMap({$0.first})
    }
}

巧妙利用 flatMap 和 Map 进行解包

比如我有下面的一个结构

struct Model {
	let age:Int?
}
let model:Model?

此时我想让age显示在文本中，你可能这么写

if let age = model?.age {
		Text("\(age)")
} else {
  	Text("")
}

但是使用flatMap和map进行解包

Text(model.flatMap({$0.age}).map({"\($0)"}) ?? "")