Maui android. Either set MainPage or override CreateWindows

In maui android app, when app was moved to back it occassionally invokes Destroy and bringing app back to front, throws an exeption:

> Either set MainPage or override CreateWindows.

 protected override void OnCreate(Bundle savedInstanceState)
 {
    base.OnCreate(savedInstanceState); <- throws here
 }

i tried to override code in App class:

 protected override Window CreateWindow(IActivationState activationState)
 {
    return base.CreateWindow(activationState); <- throws here
 }

> System.NotImplementedException: 'Either set MainPage or override
> CreateWindow.'

also tried to restore previously successfully loaded window:

 private Window _window = null;

protected override Window CreateWindow(IActivationState activationState)
{
    if (MainPage == null && _window != null)
    {
        return _window;
    }

    return _window = base.CreateWindow(activationState);
}

but app stays unresponsive after it.
Tried to use in AndroidManifest.xml options:

<manifest xmlns:android="http://schemas.android.com/apk/res/android">
<application android:networkSecurityConfig="@xml/network_security_config" android:alwaysRetainTaskState="true" android:killAfterRestore="false" android:noHistory="false" android:excludeFromRecents="false" android:persistent="true" android:allowBackup="true" android:icon="@mipmap/appicon" android:roundIcon="@mipmap/appicon_round" android:supportsRtl="true"></application>
<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
<uses-permission android:name="android.permission.INTERNET" />
<uses-permission android:name="android.permission.CAMERA" />

</manifest>
none of that had a way to prevent from destroying app.
Part of my StartupClass:

    public static MauiApp CreateMauiApp()
{
    MauiAppBuilder builder = MauiApp.CreateBuilder();

    builder.UsePrismApp<App>(prism =>
    {
        prism.RegisterTypes(containerRegistry =>
        {
            //list of pages
            containerRegistry.RegisterForNavigation<NavigationPage>();
            ....
        })
        .OnAppStart(async (containerProvider, navigationService) =>
        {
            var navService = containerProvider.Resolve<INavigationService>();
            await navService.NavigateAsync(nameof(MyPage));
        });

here i use prism over maui.
So is there any way to prevent app from destroying or to successfully restore app state on recreate?

> Maui android. Either set MainPage or override CreateWindows

About override CreateWindows, you can try to use following code:

protected override Window CreateWindow(IActivationState activationState)
{
    if (this.MainPage == null)
    {
        this.MainPage = new MainPage();
    }

    return base.CreateWindow(activationState);
}

For more info you can refer to this issue: [Android] App crashes when start from background. Wish it can help you.

I encountered the same problem myself lately. I'm using Shiny.Framework. But even the sample provided by Shiny.Framework throws the exception.

I googled some more, this comment from maui repo shows me maybe this is an emulator problem. So I created a new emulator using the latest Android 33 image, and the problem went away.

I currently find that the default iamge comes with VS 2022, which is Android 29, will always throw the exception. I tried, it seems that images above android v31 works fine.

And PS:

The exception I have also had this message:

> (Sample) ChildIndex <= -1, Parent: App Child: PrismWindow

So I think it has something to do with Prism. But I'm no expert on Prism or Shiny, so I can't dig any deeper. Hoper some one can solve this mystery.