Question

在SwiftUI中，当我在@State中定义SceneDelegate变量，然后将对应的绑定传递到所包含的ContentView时，即使@State变量被更改，该视图也永远不会更新。

如果@State变量是在ContentView中定义的，并且我将绑定传递到子视图中，则在更改var时，该子视图的更新就很好。

为什么SceneDelegate与@State不兼容？是因为它没有使用相同的主体机制吗？关于@State的事情是否仅在以后初始化，并且调用SceneDelegate的scene(scene:, willConnectTo:, options:)时生成的任何绑定都是无效的？

请注意，这似乎与Update state of a screen struct from SceneDelegate无关，https://classic.yarnpkg.com/en/docs/cli/install/不会将var放在场景委托中。

以下是视图的示例代码，该视图在计时器触发时不会更新：

import SwiftUI

struct ContentView: View {
    @Binding var s : String
    var body: some View {
        Text(s)
    }
}

class SceneDelegate: UIResponder, UIWindowSceneDelegate {

    @State var show : String = "Initial value"
    var window: UIWindow?

    func scene(_ scene: UIScene, willConnectTo session: UISceneSession, options connectionOptions: UIScene.ConnectionOptions) {

        // Pass binding to our @State var to the enclosed content view
        let contentView = ContentView(s:$show)
    
        // Set a timer to change the @State var later
        Timer.scheduledTimer(withTimeInterval: 2.0, repeats: false) { _ in
            // Explicitly run on the main queue, to rule
            // out the possibility of a queue problem
            DispatchQueue.main.async {
                self.show = "After timer"
            }
        }

        if let windowScene = scene as? UIWindowScene {
            let window = UIWindow(windowScene: windowScene)
            window.rootViewController = UIHostingController(rootView: contentView)
            self.window = window
            window.makeKeyAndVisible()
        }
    }
}

SceneDelegate中的@State vars不更新绑定视图

0 个答案: