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[Bug] NullPointerException occurs on file Xamarin.Forms.Platform.iOS\DragAndDropDelegate.cs line 125 #14602

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espritm opened this issue Sep 13, 2021 · 0 comments · Fixed by #14642
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[Bug] NullPointerException occurs on file Xamarin.Forms.Platform.iOS\DragAndDropDelegate.cs line 125 #14602

espritm opened this issue Sep 13, 2021 · 0 comments · Fixed by #14642
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@jsuarezruiz
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a/DragAndDrop i/high Completely doesn't work, crashes, or is unusably slow, has no obvious workaround; occurs less often p/iOS 🍎 t/bug 🐛
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espritm commented Sep 13, 2021 •
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Description

A null pointer exception occurs while implementing drag and drop gesture recognizer

Steps to Reproduce

A. Unit test :

  1. Call the method Xamarin.Forms.Platform.iOS.DragAndDropDelegate.SendEventArgs with a null view
  2. It crashes with a null pointer exception

B. UI Test :

  1. Get the Xamarin Forms project from github : https://github.com/espritm/Grid_Sort_Issue.git
  2. Deploy it on a iOS simulator (I tested with iPad iOS 14.5)
  3. Start a Drag gesture on a Tile, and drag over tiles until the app crashes with a null pointer exception.

Expected Behavior

The app should never crash, nothing should happen if view is null in Xamarin.Forms.Platform.iOS.DragAndDropDelegate line 125

Actual Behavior

Sometimes, the app crashes with a null pointer exception

Basic Information

  • Version with issue: Xamarin 11.16.000.174
    • iOS: Xamarin.iOS 14.20.0.25

Environment

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Microsoft Visual Studio Community 2019
Version 16.11.2
VisualStudio.16.Release/16.11.2+31624.102
Microsoft .NET Framework
Version 4.8.04084

Installed Version: Community

ADL Tools Service Provider   1.0
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ASA Service Provider   1.0

ASP.NET and Web Tools 2019   16.11.75.64347
ASP.NET and Web Tools 2019

ASP.NET Web Frameworks and Tools 2019   16.11.75.64347
For additional information, visit https://www.asp.net/

Azure App Service Tools v3.0.0   16.11.75.64347
Azure App Service Tools v3.0.0

Azure Data Lake Node   1.0
This package contains the Data Lake integration nodes for Server Explorer.

Azure Data Lake Tools for Visual Studio   2.6.1000.0
Microsoft Azure Data Lake Tools for Visual Studio

Azure Functions and Web Jobs Tools   16.11.75.64347
Azure Functions and Web Jobs Tools

Azure Stream Analytics Tools for Visual Studio   2.6.1000.0
Microsoft Azure Stream Analytics Tools for Visual Studio

C# Tools   3.11.0-4.21403.6+ae1fff344d46976624e68ae17164e0607ab68b10
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Common Azure Tools   1.10
Provides common services for use by Azure Mobile Services and Microsoft Azure Tools.

Extensibility Message Bus   1.2.6 (master@34d6af2)
Provides common messaging-based MEF services for loosely coupled Visual Studio extension components communication and integration.

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Fabric Diagnostic Events

GitHub.VisualStudio   2.11.102.28613
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IntelliCode Extension   1.0
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Microsoft JVM Debugger   1.0
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Microsoft Visual Studio Tools for Containers   1.2
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Mono Debugging for Visual Studio   16.10.15 (552afdf)
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NuGet Package Manager   5.11.0
NuGet Package Manager in Visual Studio. For more information about NuGet, visit https://docs.nuget.org/

ProjectServicesPackage Extension   1.0
ProjectServicesPackage Visual Studio Extension Detailed Info

Razor (ASP.NET Core)   16.1.0.2122504+13c05c96ea6bdbe550bd88b0bf6cdddf8cde1725
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SQL Server Data Tools   16.0.62107.28140
Microsoft SQL Server Data Tools

ToolWindowHostedEditor   1.0
Hosting json editor into a tool window

TypeScript Tools   16.0.30526.2002
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Visual Basic Tools   3.11.0-4.21403.6+ae1fff344d46976624e68ae17164e0607ab68b10
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Xamarin   16.11.000.174 (d16-11@e8f56f1)
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Xamarin Designer   16.11.0.17 (remotes/origin/11e0001f0b17269345e80b58fb3adf1ba4efe2cd@11e0001f0)
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Xamarin Templates   16.10.5 (355b57a)
Templates for building iOS, Android, and Windows apps with Xamarin and Xamarin.Forms.

Xamarin.Android SDK   11.4.0.5 (d16-11/7776c9f)
Xamarin.Android Reference Assemblies and MSBuild support.
    Mono: c633fe9
    Java.Interop: xamarin/java.interop/d16-11@48766c0
    ProGuard: Guardsquare/proguard/v7.0.1@912d149
    SQLite: xamarin/sqlite/3.35.4@85460d3
    Xamarin.Android Tools: xamarin/xamarin-android-tools/d16-11@683f375


Xamarin.iOS and Xamarin.Mac SDK   14.20.0.25 (3b53e529b)
Xamarin.iOS and Xamarin.Mac Reference Assemblies and MSBuild support.

Build Logs

Exception Stacktrace :

{System.NullReferenceException: Object reference not set to an instance of an object
at Xamarin.Forms.Platform.iOS.DragAndDropDelegate.SendEventArgs[TRecognizer] (System.Action`1[T] func, Xamarin.Forms.View view) [0x00000] in D:\a\1\s\Xamarin.Forms.Platform.iOS\DragAndDropDelegate.cs:125
at Xamarin.Forms.Platform.iOS.DragAndDropDelegate.HandleDragLeave (Xamarin.Forms.View element, Xamarin.Forms.DataPackage dataPackage) [0x00019] in D:\a\1\s\Xamarin.Forms.Platform.iOS\DragAndDropDelegate.cs:209
at Xamarin.Forms.Platform.iOS.DragAndDropDelegate.SessionDidExit (UIKit.UIDropInteraction interaction, UIKit.IUIDropSession session) [0x00041] in D:\a\1\s\Xamarin.Forms.Platform.iOS\DragAndDropDelegate.cs:70
at (wrapper managed-to-native) UIKit.UIApplication.UIApplicationMain(int,string[],intptr,intptr)
at UIKit.UIApplication.Main (System.String[] args, System.IntPtr principal, System.IntPtr delegate) [0x00005] in /Users/builder/azdo/_work/1/s/xamarin-macios/src/UIKit/UIApplication.cs:86
at UIKit.UIApplication.Main (System.String[] args, System.String principalClassName, System.String delegateClassName) [0x0000e] in /Users/builder/azdo/_work/1/s/xamarin-macios/src/UIKit/UIApplication.cs:65
at SampleApp.iOS.Application.Main (System.String[] args) [0x00001] in C:\Workspace\MyUBP\Modules\Sample\SampleApp\SampleApp.iOS\Main.cs:17 }

Screenshots

Reproduction Link

github repo : https://github.com/espritm/Grid_Sort_Issue.git
use command line : git clone https://github.com/espritm/Grid_Sort_Issue.git

Workaround

Tryied following workarounds, with no success :
In the client project, remove the DragGestureRecognizers before removing the view from the grid.
In the client project, set AllowDrop and CanDrag to false before removing the view from the grid.
@espritm espritm added s/unverified New report that has yet to be verified t/bug 🐛 labels Sep 13, 2021
@jsuarezruiz jsuarezruiz added this to New in Triage via automation Sep 13, 2021
@jsuarezruiz jsuarezruiz added i/high Completely doesn't work, crashes, or is unusably slow, has no obvious workaround; occurs less often p/iOS 🍎 and removed s/unverified New report that has yet to be verified labels Sep 13, 2021
@jsuarezruiz jsuarezruiz self-assigned this Sep 21, 2021
@jsuarezruiz jsuarezruiz moved this from New to Ready For Work in Triage Sep 21, 2021
@jsuarezruiz jsuarezruiz mentioned this issue Sep 21, 2021
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Triage automation moved this from Ready For Work to Closed Oct 2, 2021
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Labels
a/DragAndDrop i/high Completely doesn't work, crashes, or is unusably slow, has no obvious workaround; occurs less often p/iOS 🍎 t/bug 🐛
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[iOS] Fix NRE dropping element from removed view xamarin/Xamarin.Forms
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@jsuarezruiz @espritm