[Bug] InnerGestureListener IOnGestureListener.OnLongPress NullReferenceException

[schacherlj]

Description

DragGestureRecognizer is disposed before long press is processed

System.NullReferenceException: Object reference not set to an instance of an object.
IOnGestureListener.OnLongPress (Android.Views.MotionEvent e) D:\a\1\s\Xamarin.Forms.Platform.Android\InnerGestureListener.cs:120

Steps to Reproduce

1. create content page with telerik RadTabView with more tabs
2. place CollectionView on first tab
3. use grid with DragGestureRecognizer as item template
4. drag item horizontally to switch tabs
5. second tab is displayed
6. app crashes

Basic Information

• Version with issue: 5.0.0.2578
• NuGet Packages: Telerik.UI.for.Xamarin.Input 2023.1.117.1

Environment

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Microsoft Visual Studio Professional 2022
Version 17.5.1
VisualStudio.17.Release/17.5.1+33424.131
Microsoft .NET Framework
Version 4.8.04084

Installed Version: Professional

Visual C++ 2022   00483-10700-27530-AA705
Microsoft Visual C++ 2022

C# Tools   4.5.0-6.23123.11+271ccd71554f7d28d2f90551aafd0bdeb5d327aa
C# components used in the IDE. Depending on your project type and settings, a different version of the compiler may be used.

Microsoft JVM Debugger   1.0
Provides support for connecting the Visual Studio debugger to JDWP compatible Java Virtual Machines

Mono Debugging for Visual Studio   17.5.9 (11975e6)
Support for debugging Mono processes with Visual Studio.

NuGet Package Manager   6.5.0
NuGet Package Manager in Visual Studio. For more information about NuGet, visit https://docs.nuget.org/

Open Command Line   2.5.238
2.5.238

Visual C++ for Cross Platform Mobile Development (Android)   17.0.33312.129
Visual C++ for Cross Platform Mobile Development (Android)

Xamarin   17.5.0.173 (d17-5@33e727c)
Visual Studio extension to enable development for Xamarin.iOS and Xamarin.Android.

Xamarin Designer   17.5.3.46 (remotes/origin/d17-5@e4dd80b2bb)
Visual Studio extension to enable Xamarin Designer tools in Visual Studio.

Xamarin Templates   17.5.41 (ba80d05)
Templates for building iOS, Android, and Windows apps with Xamarin and Xamarin.Forms.

Xamarin.Android SDK   13.2.0.0 (d17-5/797e2e1)
Xamarin.Android Reference Assemblies and MSBuild support.
    Mono: 6dd9def
    Java.Interop: xamarin/java.interop/main@149d70fe
    SQLite: xamarin/sqlite/3.40.0@fdc1e34
    Xamarin.Android Tools: xamarin/xamarin-android-tools/main@9f02d77


Xamarin.iOS and Xamarin.Mac SDK   16.2.0.5 (7738c90c9)
Xamarin.iOS and Xamarin.Mac Reference Assemblies and MSBuild support.

Build Logs

Screenshots

Reproduction Link

Workaround

[kobbok]

I'm experiencing the same problem, for me it's happening with a CollectionView when scrolling it up and down repeatedly.

It seems the InnerGestureListener gets disposed, then the internal InnerGestureListener constructor gets called, judging from the comment above that function the gesture listener is still required by the App but since it was disposed the _dragAndDropGestureListener is now null causing the NullReferenceException.

It looks like the void GestureDetector.IOnGestureListener.OnLongPress(MotionEvent e) function in Xamarin.Forms.Platform.Android\InnerGestureListener.cs is missing a disposed check. Something like the following should fix the problem:

 void GestureDetector.IOnGestureListener.OnLongPress(MotionEvent e)
 {
+    if (_disposed)
+        return;
+
     SetStartingPosition(e);
     _dragAndDropGestureHandler.OnLongPress(e);
 }

Edit: Learned that CollectionView and DragGestureRecognizer and DropGestureRecognizer are way harder to combine than seems at first glance. Fixed my problem by using https://github.com/billvenhaus/ReorderableCollectionView.Forms amazing package
Sadly this probably doesn't fix the problem for OP