[BUG] iOS screen mirroring with popup let the app crash on opening the popup

[imuller]

Is there an existing issue for this?

• I have searched the existing issues

Did you read the "Reporting a bug" section on Contributing file?

• I have read the "Reporting a bug" section on Contributing file: https://github.com/CommunityToolkit/Maui/blob/main/CONTRIBUTING.md#reporting-a-bug

Current Behavior

When opening a Popup when screen mirroring is active. The app crashes with a System.InvalidOperationException.

System.InvalidOperationException: ViewController cannot be null. at CommunityToolkit.Maui.Core.Views.MauiPopup.SetElement(IPopup element) in /_/src/CommunityToolkit.Maui.Core/Views/Popup/MauiPopup.macios.cs:line 80 at CommunityToolkit.Maui.Core.Handlers.PopupHandler.ConnectHandler(MauiPopup platformView) in /_/src/CommunityToolkit.Maui.Core/Handlers/Popup/PopupHandler.macios.cs:line 91 at Microsoft.Maui.Handlers.ElementHandler2[[CommunityToolkit.Maui.Core.IPopup, CommunityToolkit.Maui.Core, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null],[CommunityToolkit.Maui.Core.Views.MauiPopup, CommunityToolkit.Maui.Core, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null]].OnConnectHandler(Object platformView)
at Microsoft.Maui.Handlers.ElementHandler.ConnectHandler(Object platformView)
at Microsoft.Maui.Handlers.ElementHandler.SetVirtualView(IElement view)
at Microsoft.Maui.Controls.Element.SetHandler(IElementHandler newHandler)
at Microsoft.Maui.Controls.Element.set_Handler(IElementHandler value)
at Microsoft.Maui.Platform.ElementExtensions.ToHandler(IElement view, IMauiContext context)
at CommunityToolkit.Maui.Views.PopupExtensions.CreatePopup(Page page, Popup popup) in //src/CommunityToolkit.Maui/Views/Popup/PopupExtensions.shared.cs:line 89
at CommunityToolkit.Maui.Views.PopupExtensions.CreateAndShowPopupAsync[ToolkitPopupPage](Page page, ToolkitPopupPage popup) in //src/CommunityToolkit.Maui/Views/Popup/PopupExtensions.shared.cs:line 113
at CommunityToolkit.Maui.Views.PopupExtensions.ShowPopupAsync[ToolkitPopupPage](Page page, ToolkitPopupPage popup) in /_/src/CommunityToolkit.Maui/Views/Popup/PopupExtensions.shared.cs:line 57
at MauiApp1.MainPage.OnOpenToolkitPopupPage(Object sender, EventArgs e) in /Users/user/RiderProjects/MauiApp1/MauiApp1/MainPage.xaml.cs:line 24
at System.Threading.Tasks.Task.<>c.b__128_0(Object )
at Foundation.NSAsyncSynchronizationContextDispatcher.Apply()
at UIKit.UIApplication.UIApplicationMain(Int32 , String[] , IntPtr , IntPtr )
at UIKit.UIApplication.Main(String[] , Type , Type )
at MauiApp1.Program.Main(String[] args) in /Users/user/RiderProjects/MauiApp1/MauiApp1/Platforms/iOS/Program.cs:line 13`

Expected Behavior

The popup should behave the same as on the device. This is very annoying when demo MAUI apps when the app crashes.

Steps To Reproduce

1. Create a Popup in you're application
2. Add a button that opens the popup
3. Start screen mirroring on the device (i've tested it on an iPad with iOS 16.4)
4. Open the app
5. Click the button that opens the popup
6. The app crashes...

Link to public reproduction project repository

https://github.com/imuller/app-popups-problem

Environment

- .NET MAUI CommunityToolkit: 5.1.0
- OS: iOS 16.4 running on and iPad Pro
- .NET MAUI: 7.0.81

Anything else?

No response

Hi @imuller. We have added the "needs reproduction" label to this issue, which indicates that we cannot take further action. This issue will be closed automatically in 5 days if we do not hear back from you by then - please feel free to re-open it if you come back to this issue after that time.

[imuller]

I added a project: https://github.com/imuller/app-popups-problem

[pbhatt-nucor]

Any updates on this thread? I have faced the same issue with iPhone 16 (OS version 17.1.1) & screen mirroring. I'm using .Net MAUI 7.0

ViewController cannot be null.
CommunityToolkit.Maui.Core.Views.MauiPopup.SetElement(IPopup element)
CommunityToolkit.Maui.Core.Handlers.PopupHandler.ConnectHandler(MauiPopup platformView)
Microsoft.Maui.Handlers.ElementHandler`2[[CommunityToolkit.Maui.Core.IPopup, CommunityToolkit.Maui.Core, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null],[CommunityToolkit.Maui.Core.Views.MauiPopup, CommunityToolkit.Maui.Core, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null]].OnConnectHandler(Object platformView)
Microsoft.Maui.Handlers.ElementHandler.SetVirtualView(IElement view)
Microsoft.Maui.Controls.Element.SetHandler(IElementHandler newHandler)
Microsoft.Maui.Controls.Element.set_Handler(IElementHandler value)

[softlion]

That's because the code in Platform.GetCurrentUIViewController for iOS is too naive. It's not an issue with communitytoolkit, but with maui.

Most of the time, this is caused by a popup/dialog/alert view trying to display over an existing popup/dialog/alert view (or a not yet disappeared top level window because disappearing is animated).

So updating your own code to make sure that does not happen is the best bet.

The good new is, you can override the buggy implementation of IWindowStateManager.

The current maui implementation is here:

public UIViewController? GetCurrentUIViewController()
{
	var viewController = getCurrentController?.Invoke();

	if (viewController != null)
		return viewController;

	var window = GetKeyWindow();

	if (window != null && window.WindowLevel == UIWindowLevel.Normal)
		viewController = window.RootViewController;

	if (viewController == null)
	{
		window = GetWindows()?
			.OrderByDescending(w => w.WindowLevel)
			.FirstOrDefault(w => w.RootViewController != null && w.WindowLevel == UIWindowLevel.Normal);

		viewController = window?.RootViewController;
	}

	while (viewController?.PresentedViewController != null)
		viewController = viewController.PresentedViewController;

	return viewController;
}

The bad news is, WindowStateManager.SetDefault() is internal. And also the fixed implementation has still to be provided.

If a contributor wants to check, he/she can use the windows store app "AirPlay Screen Mirroring Receiver" as an airplay receiver for screen mirrorring, to test that implementation.

[zeldafreak]

I think I was able to work around this issue thanks to @softlion and this PR over here: rotorgames/Rg.Plugins.Popup#754

While we can't provide our own implementation of IWindowStateManager that properly selects the correct UIWindow and UIViewController, it seems you can use WindowStateManager.Default.Init and pass in a delegate for GetCurrentUIViewController that will be favored over the default implementation.

My personal approach was to sort the UIWindowScene's by their UIWindowSceneSessionRole:

using var scenes = UIApplication.SharedApplication.ConnectedScenes;
var windowScene = scenes.ToArray<UIWindowScene>()
                        .MinBy(scene => (int)scene.Session.Role); // favor "Application" over other roles.
return windowScene?.Windows.FirstOrDefault();

This works because Application has a value of 0, so all the others, like ExternalDisplay (which is the role of the AirPlay scene) will always come after it.

I have no idea if I will run into some other kind of issue in the future by doing this-- I'm not an iOS developer. But if I'm lucky I won't be humiliated by intermittent crashes when demonstrating progress on my project like I was this morning.

Thank you so much, @softlion and @EmilienDup !

[softlion]

@zeldafreak A better way would be to get the MainPage from maui, and get its window instead. Why try to guess something when we already have it. no ?

[zeldafreak]

@softlion I admit I don't fully understand the ramifications of changing how it works now, so I erred on the side of making as few changes as possible. Leaving all the existing logic in place and merely adjusting how it handles the case where there are multiple scenes seemed like the safest solution at the time. But to your point, this is supposed to get the "root" view controller, and so going directly to the MainPage's Window does seem appropriate.

Are you suggesting:

private static UIWindow? GetKeyWindow()
{
    // Use the MainPage's Window as the key Window if it exists.
    if (Microsoft.Maui.Controls.Application.Current?.MainPage?.Window?.Handler?.PlatformView is UIWindow window)
    {
        return window;
    }

    // if we have scene support, use that
    if (OperatingSystem.IsIOSVersionAtLeast(13) || OperatingSystem.IsMacCatalystVersionAtLeast(13))
    {
        try
        {
            using var scenes = UIApplication.SharedApplication.ConnectedScenes;
            var windowScene = scenes.ToArray<UIWindowScene>()
                                    .MinBy(scene => (int)scene.Session.Role); // favor "Application" over other roles.
            return windowScene?.Windows.FirstOrDefault();
        }
        catch (InvalidCastException)
        {
            // HACK: Workaround for https://github.com/xamarin/xamarin-macios/issues/13704
            //       This only throws if the collection is empty.
            return null;
        }
    }

    // use the windows property (up to 13.0)
    return UIApplication.SharedApplication.KeyWindow;
}

... which will still fall back to looking at all the scenes for an appropriate window if it can't find one, but tries first to get MAUI's application window...

[devinduplessis]

@zeldafreak I know this has been a while but this issue is plagueing my app as well. How could I ovveride the default implementation. By injectecting my own WindowsStateManager with the changes or some other way?

[zeldafreak]

@devinduplessis I'll put my code below for your sake and any others who suffer the same issue. But first I want to express frustration that it took less than 2 weeks for DevExpress to have a hotfix for the same issue. By using a decompiler, I know they added a single expression, a ~20 character change, and now all of their controls are immune to this problem. Meanwhile, this issue has been ignored for a year by the MAUI team. (EDIT: To clarify, this is not a Toolkit bug, it's a MAUI bug.)

Here's the entirety of my /Platforms/iOS/AppDelegate.cs file. I copy/pasted almost all of this from MAUI's WindowStateManagerImplementation and then made as few changes as possible. But if you return null, it'll fall back on the default behavior, so where this code is identical to WindowStateManagerImplementation, I could've returned null rather than duplicate MAUI/Xamarin's behavior. I apologize for how unnecessarily long this is, but I've been using it for over a month now and it's never crashed on me, so I'm giving it to you as-is.

[Register("AppDelegate")]
public class AppDelegate : MauiUIApplicationDelegate
{
    protected override MauiApp CreateMauiApp()
    {
        var app = MauiProgram.CreateMauiApp();

        // Give WindowStateManager a default implementation for retrieving the UIViewController.
        // If specified, it will try this function first. The default behavior will be used if it returns null.
        WindowStateManager.Default.Init(GetCurrentUIViewController);

        return app;
    }

    private static UIViewController? GetCurrentUIViewController()
    {
        var window = GetKeyWindow();

        UIViewController? viewController = null;
        if (window != null && window.WindowLevel == UIWindowLevel.Normal)
            viewController = window.RootViewController;

        if (viewController == null)
        {
            window = GetWindows()?
                     .OrderByDescending(w => w.WindowLevel)
                     .FirstOrDefault(w => w.RootViewController != null && w.WindowLevel == UIWindowLevel.Normal);

            viewController = window?.RootViewController;
        }

        while (viewController?.PresentedViewController != null)
            viewController = viewController.PresentedViewController;

        return viewController;
    }

    private static UIWindow? GetKeyWindow()
    {
        // Prefer the MainPage window, per @softlion: https://github.com/CommunityToolkit/Maui/issues/1158#issuecomment-2002395273
        if (Microsoft.Maui.Controls.Application.Current?.MainPage?.Window?.Handler?.PlatformView is UIWindow window)
        {
            return window;
        }

        // if we have scene support, use that
        if (OperatingSystem.IsIOSVersionAtLeast(13) || OperatingSystem.IsMacCatalystVersionAtLeast(13))
        {
            try
            {
                using var scenes = UIApplication.SharedApplication.ConnectedScenes;
                var windowScene = scenes.ToArray<UIWindowScene>()
                                        .MinBy(scene => (int)scene.Session.Role); // favor "Application" over other roles.
                return windowScene?.Windows.FirstOrDefault();
            }
            catch (InvalidCastException)
            {
                // HACK: Workaround for https://github.com/xamarin/xamarin-macios/issues/13704
                //       This only throws if the collection is empty.
                return null;
            }
        }

        // use the windows property (up to 13.0)
        return UIApplication.SharedApplication.KeyWindow;
    }

    private static UIWindow[]? GetWindows()
    {
        // if we have scene support, use that
        if (OperatingSystem.IsIOSVersionAtLeast(13) || OperatingSystem.IsMacCatalystVersionAtLeast(13))
        {
            try
            {
                using var scenes = UIApplication.SharedApplication.ConnectedScenes;
                var windowScene = scenes.ToArray<UIWindowScene>()
                                         .MinBy(scene => (int)scene.Session.Role); // favor "Application" over other roles.
                return windowScene?.Windows;
            }
            catch (InvalidCastException)
            {
                // HACK: Workaround for https://github.com/xamarin/xamarin-macios/issues/13704
                //       This only throws if the collection is empty.
                return null;
            }
        }

        // use the windows property (up to 15.0)
        return UIApplication.SharedApplication.Windows;
    }
}

All credit for this workaround should go to @softlion and @EmilienDup. I may never have gotten this working (nor been able to advise DevExpress on how to fix their related bug) without their guidance/example. (but also, this isn't their code, so any bugs in it are entirely my fault 🙂)