ios - SwiftUI .onAppear，只运行一次

Question

在 SwiftUI应用程序我有这样的代码:

var body: some View {
    VStack {
        Spacer()
        ........
    }
    .onAppear {
      .... I want to have some code here ....
      .... to run when the view appears ....
    }
}

我的问题是我想在 .onAppear block 内运行一些代码，以便在应用程序出现在屏幕上、启动后或在后台运行一段时间后运行它。但似乎这段代码只在应用程序启动时运行一次，之后再也不运行了。我错过了什么吗？或者我应该使用不同的策略来获得我想要的结果？

Answer 1

当应用程序进入前台并使用 @Published 发布它时，您必须观察该事件。到ContentView .就是这样:

struct ContentView: View {

    @ObservedObject var observer = Observer()

    var body: some View {
        VStack {
            Spacer()
            //...
        }
        .onReceive(self.observer.$enteredForeground) { _ in
            print("App entered foreground!") // do stuff here
        }
    }
}

class Observer: ObservableObject {

    @Published var enteredForeground = true

    init() {
        if #available(iOS 13.0, *) {
            NotificationCenter.default.addObserver(self, selector: #selector(willEnterForeground), name: UIScene.willEnterForegroundNotification, object: nil)
        } else {
            NotificationCenter.default.addObserver(self, selector: #selector(willEnterForeground), name: UIApplication.willEnterForegroundNotification, object: nil)
        }
    }

    @objc func willEnterForeground() {
        enteredForeground.toggle()
    }

    deinit {
        NotificationCenter.default.removeObserver(self)
    }
}