Fix crash when closing Windows based app when using TitleBar

[MFinkBK]

Description of Change

The crash in #32194 occurs because WindowRootView.UpdateTitleBarContentSize() is called after the title bar window is already detached, but the AppWindowId property is still set. the fix is to reset the AppWindowId when the root view is cleared.

Issues Fixed

Fixes #32194

[jfversluis]

/azp run maui-pr

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[MFinkBK]

As mentioned in #32589, I wasn't sure if it fixes things, so I did look into the code and developed this PR. I tested this PR successfully.

[jfversluis]

Review Summary

The fix correctly identifies the root cause: AppWindowId remains set after the window is detached, causing UpdateTitleBarContentSize() to call InputNonClientPointerSource.GetForWindowId() with a stale window ID.

However, the line needs to be moved earlier in the Disconnect() method.

Issue: Ordering — AppWindowId cleared too late

Setting _rootView.Content = null can trigger a synchronous WinUI LayoutUpdated event, which calls UpdateTitleBarContentSize() while AppWindowId still holds the stale value — the exact crash this PR aims to fix.

Current ordering in this PR:

_rootView.Content = null;          // ← can trigger synchronous LayoutUpdated
_rootView.AppWindowId = null;      // ← too late if layout already fired above
_disconnected = true;

Suggested fix — move AppWindowId = null before any content clearing:

_rootView.AppWindowId = null;      // Neutralize first

if (_rootView.Content is RootNavigationView navView)
    navView.Content = null;

_rootView.Content = null;
_disconnected = true;

This is safe because UpdateTitleBarContentSize() already guards all AppWindowId usage with .HasValue checks, so it will simply no-op.

Minor suggestion (not blocking)

The PlatformView_LayoutUpdated event handler subscribed in SetTitleBar() is not unsubscribed during Disconnect(). Consider calling _rootView.SetTitleBar(null, null) or adding a dedicated cleanup to fully prevent post-disconnect callbacks.

[dotnet-policy-service]

Hi @@MFinkBK. We have added the "s/pr-needs-author-input" label to this issue, which indicates that we have an open question/action for you before we can take further action. This PRwill be closed automatically in 14 days if we do not hear back from you by then - please feel free to re-open it if you come back to this PR after that time.

[github-actions]

🚀 Dogfood this PR with:

⚠️ WARNING: Do not do this without first carefully reviewing the code of this PR to satisfy yourself it is safe.

curl -fsSL https://raw.githubusercontent.com/dotnet/maui/main/eng/scripts/get-maui-pr.sh | bash -s -- 34032

Or

• Run remotely in PowerShell:

iex "& { $(irm https://raw.githubusercontent.com/dotnet/maui/main/eng/scripts/get-maui-pr.ps1) } 34032"

[MFinkBK]

@jfversluis Thanks for the analysis! I did the suggested changes and re-tested with the Sandbox app. The changes still fix the crashing bug when closing the app.

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