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I am capturing Android touch gestures in a child control of ScrollView. Everything works well but under specific conditions I receive ACTION_CANCEL and stop receiving touch events. I narrowed this down to the Xamarin.Forms ScrollView. It happens under these conditions:
1. I touch the screen with 2 fingers
2. I can move one finger up and down and left and right and continue receiving events
3. I can move the second finger up and down and continue to receive events
4. When I move the second finger left or right, I receive ACTION_CANCEL
This happens even though the scroll view is not able to scroll (small content) and even though I disabled ScrollView capturing by settings InputTransparent in the PCL and doing this in a subclassed renderer:
public override bool OnInterceptTouchEvent(MotionEvent ev)
Conclusion: there is a bug in the Android ScrollView renderer which causes the ACTION_CANCEL when it should not. When I replace the ScrollView with another container control the problem goes away.
I am hoping someone can see this bug just by looking at code but if necessary I can create a sample project to show this.
I managed to replicate this with single finger tough as well. I have a vertical ScrollView and am able to move child elements using vertical finger movement, but the moment the finger moves left or right, ACTION_CANCEL is received and gesture notifications stop.
This is pointing very strongly at being a ScrollView bug
Thank you for your feedback! I will make sure it gets passed along to the appropriate person! :)
This appears to be fixed in 18.104.22.16865-pre1 but it's difficult to verify because of https://bugzilla.xamarin.com/show_bug.cgi?id=26665