navigation - 如何在 OnAppearing() 方法中导航？

Question

我想避免将我的 OnBoarding View 放在导航堆栈中，以解决按下后退按钮的问题。在我的 MainPage 中，我检查 OnBoarding 是否应该出现。如果为真，我将在 OnAppearing 方法中调用 PushModalAsync 方法。但是应用程序崩溃并出现以下异常:

Objective-C exception thrown.  Name: System.InvalidOperationException Reason: Window should have a UIWindow set. (System.InvalidOperationException)
   at Microsoft.Maui.Controls.Window.get_NativeWindow()
   at Microsoft.Maui.Controls.Platform.ModalNavigationManager.EndEditing()
   at Microsoft.Maui.Controls.Platform.ModalNavigationManager.PushModalAsync(Page modal, Boolean animated)
   at Microsoft.Maui.Controls.Window.NavigationImpl.OnPushModal(Page modal, Boolean animated)
   at BytePesaApp.MainPage.OnAppearing() in MainPage.xaml.cs:line 18
   at System.Threading.Tasks.Task.<>c.<ThrowAsync>b__128_0(Object state)
   at Foundation.NSAsyncSynchronizationContextDispatcher.Apply()

代码实现如下:

public partial class MainPage : ContentPage
{

    public MainPage()
    {
        InitializeComponent();
    }

    protected override async void OnAppearing()
    {
        base.OnAppearing();

        if (ShouldShowOnBoardingPage() == true)
        {
            await Navigation.PushModalAsync(new OnBoardingPage(), false);
        }
    }


    private bool ShouldShowOnBoardingPage()
    {
        return VersionTracking.IsFirstLaunchEver;
    }
}

Answer 1

在 OnAppearing 完成之前，Maui 似乎不适合导航。像这样推迟导航:

Dispatcher.Dispatch(async() =>
    await Navigation.PushModalAsync(new OnBoardingPage(), false);
);

此代码将被排队，并将在 OnAppearing 返回后运行。

---

替代方案是在入职期间替换主页。
在 App.xaml.cs 中:

if (ShouldShowOnBoardingPage() == true)
    MainPage = new OnBoardingPage();
else
    MainPage = new MainPage();

然后当 OnBoarding 完成时:

    Application.Current.MainPage = new MainPage();

如果可能的话，我更喜欢后一种方法。