onAppear doesn't trigger

ON外观不会触发

struct ProfileView: View {
    @StateObject var viewModel = ProfileViewViewModel()
    var body: some View {
        NavigationView {
            VStack {
                if let user = viewModel.user {
                    profile(user: user)
                } else {
                    Text("Loading Profile...")
                }
            }
            .navigationTitle("Profile")
        }
        .onAppear {
            viewModel.fetchUser() //this is the problem
        }
        .fullScreenCover(isPresented: $viewModel.showingPreview) {
            PreviewAvatarView()
        }
    }
}

I realized that onAppear didn't trigger when I dismiss fullscreencover.

我意识到，当我关闭全屏封面时，onAppar并没有触发。

Instead of using onAppear you can use task.

您可以使用TASK，而不是使用onOuar。

struct ProfileView: View {
    @StateObject var viewModel = ProfileViewViewModel()
    var body: some View {
        NavigationView {
            VStack {
                if let user = viewModel.user {
                    profile(user: user)
                } else {
                    Text("Loading Profile...")
                }
            }
            .navigationTitle("Profile")
        }
        .task(id: viewModel.showingPreview) {
            guard !viewModel.showingPreview else {return} //Check for false
    
            viewModel.fetchUser() //this is the problem
        }
        .fullScreenCover(isPresented: $viewModel.showingPreview) {
            PreviewAvatarView()
        }
    }
}

task will run onAppear and when the Bool is false.

task将在onAppear和Bool为false时运行。

The onAppear doesn’t trigger because your underlying view is not appearing – the view that is covering it is going away, which isn’t the same thing.

OnAppar不会触发，因为底层视图没有出现--覆盖它的视图正在消失，这不是一回事。

However, fullScreenCover has a rarely-used optional argument, onDismiss, which may fulfil your needs, e.g.:

但是，fullScreenCover有一个很少使用的可选参数onDismi，它可能会满足您的需求，例如：

.fullScreenCover(
  isPresented: $viewModel.showingPreview,
  onDismiss: { viewModel.fetchUser() }
) {
  PreviewAvatarView()
}

Apple documentation

Apple文档

You can try this solution.

你可以试试这个解决方案。

struct ProfileView: View {
    @StateObject var viewModel = ProfileViewViewModel()
    var body: some View {
        NavigationView {
            VStack {
                if let user = viewModel.user {
                    profile(user: user)
                } else {
                    Text("Loading Profile...")
                }
            }
            .navigationTitle("Profile")
        }
        .onAppear {
            viewModel.fetchUser() //this is the problem
        }
        .fullScreenCover(isPresented: $viewModel.showingPreview) {
            PreviewAvatarView()
        }
        .onChange(of: viewModel.showingPreview) { isFullScreenOpen in
            if !isFullScreenOpen {
                viewModel.fetchUser()
            }//Executed only when full screen cover is closed.
        }
    }
}

Whenever the sheet closes the viewModel.fetchUser() will be executed.

每当工作表关闭时，都将执行viewModel.fetchUser()。