Switching to an existing page with SetTitleView used in Flyout menu causes "Element is already the child of another element" crash on Windows in MAUI 8.0.6

[SmartmanApps]

Description

In MAUI 8.0.3, the TitleBar was broken for NavigationPages, but otherwise switching between existing (i.e. not "new" each time) was working. In 8.0.6 the former was fixed but the latter is now broken on Windows. Bug also present in 8.0.7. It still works if...

• on Android (not tested other platforms)
• if you create a new page each time (which defeats the purpose of using a Flyout menu)
• if you use "Title=" instead of NavigationPage.SetTitleView
• in 8.0.3
  But not if you've used SetTitleView on an existing page in Windows with 8.0.6-7.

Note: the repro repo is the same one as I used for 15767, which is still not fixed (I added the new code in a new branch).

Steps to Reproduce

1. create a new MAUI app with a Flyout menu, which has at least 1 page in it which is only created once.
2. use SetTitleView on at least one of those such pages.
3. that page(s) will work the first time you switch to it, but when you switch to another page and then switch back to it the crash occurs on Windows.
4. the code for all this is in the 806issue branch of the FlyoutRepro repo. You can change the commnted-out lines on both TemplateFlyoutPage.cs and SecondPage.cs to change the various configs (currently set to it's crashing state of using SetTitleView and only creating the page once). I have some //// comments just before those lines you can change (so just search for ////).

Link to public reproduction project repository

https://github.com/SmartmanApps/FlyoutRepro

Version with bug

8.0.6 SR1

Is this a regression from previous behavior?

Yes, this used to work in .NET MAUI

Last version that worked well

8.0.3 GA

Affected platforms

Windows

Affected platform versions

1000.19041.1000.0

Did you find any workaround?

See description - changing any one of the 4 factors (existing page, Windows, SetTitleView, 8.0.6) works, just not those 4 things together.

Relevant log output

Exception thrown: 'System.Runtime.InteropServices.COMException' in WinRT.Runtime.dll
WinRT information: Element is already the child of another element.
'FlyoutRepro.exe' (CoreCLR: clrhost): Loaded 'C:\Program Files\dotnet\shared\Microsoft.NETCore.App\8.0.2\System.Diagnostics.StackTrace.dll'. 
'FlyoutRepro.exe' (CoreCLR: clrhost): Loaded 'C:\Program Files\dotnet\shared\Microsoft.NETCore.App\8.0.2\System.Reflection.Metadata.dll'. 
'FlyoutRepro.exe' (CoreCLR: clrhost): Loaded 'C:\Program Files\dotnet\shared\Microsoft.NETCore.App\8.0.2\System.Collections.Immutable.dll'. 
********************************** UNHANDLED EXCEPTION! Details: System.Runtime.InteropServices.COMException (0x800F1000): No installed components were detected.

Element is already the child of another element.
   at WinRT.ExceptionHelpers.<ThrowExceptionForHR>g__Throw|39_0(Int32 hr)
The program '[23644] FlyoutRepro.exe' has exited with code 4294967295 (0xffffffff).

[SmartmanApps]

P.S. this happens regardless of what type of view is used in the TitleView. e.g. I was initially using a HorizontalStackLayout, but I tried it also with a Label and the same thing happened.

[RoiChen001]

This issue can be reproduced on Windows platform on the latest 17.12.0 Preview 1.0(8.0.80 & 8.0.6), but this used to work in 8.0.3.

[davidW83]

I have the same issue with a complex App transferred from Xamarin to MAUI.
I started using

TitleView

because on WINIU the default Toolbar FontSize is way to huge, a custom View seemed like the way to go. But i encountered the same error as above.

I just wanted to add my attempt for a solution, to compare it with others and/or if there any drawbacks or a better one. :)

Solution:

• Before i change the FlayoutPage.DetailPage with another selected page, i set the TitleView again by "NavigationPage.SetTitleView" . So far i had no issues.

NavigationPage.SetTitleView(selectedPage, viewtemplate);
Detail = selectedPage;

My questions :

• Are there any drawbacks doing it this way?
  Should i call 'NavigationPage.GetView' before i do this and null the returned view if i select the same page again or is any overwritten view disposed? I'm afraid of memory leaks overtime , althoug this is just a small viewtemplate.

var prexistingView = NavigationPage.GetTitleView(thselectedPages);
prexistingView .Parent = null;
prexistingView .DisconnectHandlers();
prexistingView = null;

And I have to add, i don't create a new Page every time, the Flyout seems more stable that way if the user switches the detail page often.

PS: i am currently on MAUI9 9.0.12

[omghb]

We see the same issue after migrating from MAUI 8.0.93 to MAUI 9.0.40.

In our case we set the CollectionView.EmptyView in XAML to a custom control.

If we navigate a second time to this page we get the exception Element is already the child of another element on Windows. The same navigation works fine on Android and iOS.

Workaround in code-behind:

protected override void OnAppearing()
{
    base.OnAppearing();
    collectionView.EmptyView = new CustomEmptyView();
}

protected override void OnDisappearing()
{
    collectionView.EmptyView = null;
    base.OnDisappearing();
}

UPDATE
Probably this is not the same issue than described here. So created an own issue for this one:

• Using CollectionView.EmptyView results in an Exception on Windows #28212