[BUG] iOS: Slider unresponsive if parent view has TouchBehavior

[jurganson]

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

The first tap and drag works, however after that the slider remains unresponsive.
https://github.com/user-attachments/assets/accc4a03-2ab6-49a1-9b89-1e124b76719f

Expected Behavior

The Slider should work regardless of a behavior in the parent view.

Steps To Reproduce

1. Open and run the reproduction repo on a iOS device
2. Observe the bug

Link to public reproduction project repository

https://github.com/jurganson/iOS_Slider_Broken_Inside_TouchBehavior_View

Environment

- .NET MAUI CommunityToolkit: 8.0.1
- OS: iOS
- .NET MAUI: 8.0.4

Anything else?

No response

[jurganson]

As a workaround, it seems like setting DelaysTouchesEnded in the general UIGestureRecognizer fixes the issue:

Changes done in this file:

sealed class TouchUITapGestureRecognizer : UIGestureRecognizer
	{
		readonly TouchBehavior behavior;

		float? defaultRadius;
		float? defaultShadowRadius;
		float? defaultShadowOpacity;
		CGPoint? startPoint;

		bool isCanceled;

		public TouchUITapGestureRecognizer(TouchBehavior behavior)
		{
			this.behavior = behavior;
			CancelsTouchesInView = false;

                        // Workaround
			DelaysTouchesEnded = false; // *Fixes* the github issue
			DelaysTouchesBegan = false; // *Fixes* similar issues with Slider in own project

			Delegate = new TouchUITapGestureRecognizerDelegate();
		}

  ... 

So it seems like the UIGestureRecognizer is not allowing for the Up event to pass down to its subsequent view, because it gets stuck in validating if it can consume it - even though we allow it to pass it down using CancelsTouchesInView. Could there internally be happening an error in Xamarin.iOS which causes the Up event to get 'stuck'?