[Bug] Null Reference in ListView OnCommandCanExecuteChanged

[AlfonChitoSalano]

Description

System.NullReferenceException: Object reference not set to an instance of an object in ListView.OnCommandCanExecuteChanged (System.Object sender, System.EventArgs eventArgs)

Steps to Reproduce

Just happened in our production and we saw in our appcenter logs. Our user just pressed back button then this error showed.

ListView.OnCommandCanExecuteChanged (System.Object sender, System.EventArgs eventArgs)
(wrapper delegate-invoke) .invoke_void_object_EventArgs(object,System.EventArgs)
DelegateCommandBase+<>c__DisplayClass7_0.b__0 (System.Object o)
SyncContext+<>c__DisplayClass2_0.b__0 ()
Thread+RunnableImplementor.Run ()
IRunnableInvoker.n_Run (System.IntPtr jnienv, System.IntPtr native__this)
(wrapper dynamic-method) Android.Runtime.DynamicMethodNameCounter.75(intptr,intptr)

Expected Behavior

There will be no crash because the RefreshCommand in the method OnCommandCanExecuteChanged was null. https://github.com/xamarin/Xamarin.Forms/blob/caab66bcf9614aca0c0805d560a34e176d196e17/Xamarin.Forms.Core/ListView.cs

Actual Behavior

When the user press back button and we have a listview in the previous page, then our app crashed.

Basic Information

• Version with issue: 5.0.0.2012
• Last known good version: No idea
• Platform Target Frameworks:
  • Android: Xamarin.Android SDK 11.3.0.1
• Affected Devices: Android

Environment

Microsoft Visual Studio Community 2019
Version 16.10.0
VisualStudio.16.Release/16.10.0+31321.278
Microsoft .NET Framework
Version 4.8.04084

Installed Version: Community

Visual C++ 2019 00435-60000-00000-AA042
Microsoft Visual C++ 2019

.NET Core Debugging with WSL 2 1.0
.NET Core Debugging with WSL 2

ADL Tools Service Provider 1.0
This package contains services used by Data Lake tools

ASA Service Provider 1.0

ASP.NET and Web Tools 2019 16.10.525.31942
ASP.NET and Web Tools 2019

ASP.NET Web Frameworks and Tools 2019 16.10.525.31942
For additional information, visit https://www.asp.net/

Azure App Service Tools v3.0.0 16.10.525.31942
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 16.10.525.31942
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 3.10.0-4.21269.26+029847714208ebe49668667c60ea5b0a294e0fcb
C# components used in the IDE. Depending on your project type and settings, a different version of the compiler may be used.

Common Azure Tools 1.10
Provides common services for use by Azure Mobile Services and Microsoft Azure Tools.

Deveroom for SpecFlow 1.0
Visual Studio extension for working with SpecFlow projects and Gherkin feature files.

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

Fabric.DiagnosticEvents 1.0
Fabric Diagnostic Events

IntelliCode Extension 1.0
IntelliCode Visual Studio Extension Detailed Info

Microsoft Azure HDInsight Azure Node 2.6.1000.0
HDInsight Node under Azure Node

Microsoft Azure Hive Query Language Service 2.6.1000.0
Language service for Hive query

Microsoft Azure Service Fabric Tools for Visual Studio 16.10
Microsoft Azure Service Fabric Tools for Visual Studio

Microsoft Azure Stream Analytics Language Service 2.6.1000.0
Language service for Azure Stream Analytics

Microsoft Azure Stream Analytics Node 1.0
Azure Stream Analytics Node under Azure Node

Microsoft Azure Tools 2.9
Microsoft Azure Tools for Microsoft Visual Studio 2019 - v2.9.40423.1

Microsoft Continuous Delivery Tools for Visual Studio 0.4
Simplifying the configuration of Azure DevOps pipelines from within the Visual Studio IDE.

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

Microsoft Library Manager 2.1.113+g422d40002e.RR
Install client-side libraries easily to any web project

Microsoft MI-Based Debugger 1.0
Provides support for connecting Visual Studio to MI compatible debuggers

Microsoft Visual C++ Wizards 1.0
Microsoft Visual C++ Wizards

Microsoft Visual Studio Tools for Containers 1.2
Develop, run, validate your ASP.NET Core applications in the target environment. F5 your application directly into a container with debugging, or CTRL + F5 to edit & refresh your app without having to rebuild the container.

Microsoft Visual Studio VC Package 1.0
Microsoft Visual Studio VC Package

Mono Debugging for Visual Studio 16.10.15 (552afdf)
Support for debugging Mono processes with Visual Studio.

Node.js Tools 1.5.30310.1 Commit Hash:e550dd1b679956810ccace4368dbc7a64443213b
Adds support for developing and debugging Node.js apps in Visual Studio

NuGet Package Manager 5.10.0
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
Provides languages services for ASP.NET Core Razor.

SQL Server Data Tools 16.0.62105.04180
Microsoft SQL Server Data Tools

StylerPackage Extension 1.0
StylerPackage Visual Stuido Extension Detailed Info

Syncfusion ASP.NET Core Project Templates 16.1.0.32
Provides project templates for creating an ASP.NET Core Web Application using Syncfusion ASP.NET Core components.

Syncfusion EJ2 Web Conversion and Migration 13.4.0.53
Converts and migrates a web project into a Syncfusion web project.

SyncfusionMenu Extension 1.0
SyncfusionMenu Visual Studio Extension Detailed Info

ToolWindowHostedEditor 1.0
Hosting json editor into a tool window

TypeScript Tools 16.0.30429.2002
TypeScript Tools for Microsoft Visual Studio

Visual Basic Tools 3.10.0-4.21269.26+029847714208ebe49668667c60ea5b0a294e0fcb
Visual Basic components used in the IDE. Depending on your project type and settings, a different version of the compiler may be used.

Visual F# Tools 16.10.0-beta.21262.7+1b23bbeda88ea3cb9be9af777f4c99fa8663df81
Microsoft Visual F# Tools

Visual Studio Code Debug Adapter Host Package 1.0
Interop layer for hosting Visual Studio Code debug adapters in Visual Studio

Visual Studio Container Tools Extensions 1.0
View, manage, and diagnose containers within Visual Studio.

Visual Studio Tools for Containers 1.0
Visual Studio Tools for Containers

Visual Studio Tools for Kubernetes 1.0
Visual Studio Tools for Kubernetes

Visual Studio Tools for Unity 4.10.2.0
Visual Studio Tools for Unity

VisualStudio.DeviceLog 1.0
Information about my package

VisualStudio.Foo 1.0
Information about my package

VisualStudio.Mac 1.0
Mac Extension for Visual Studio

Xamarin 16.10.000.228 (d16-10@1c8354c)
Visual Studio extension to enable development for Xamarin.iOS and Xamarin.Android.

Xamarin Designer 16.10.0.115 (remotes/origin/c750fbf1bde3c720d077f51640fe197c6dac7cbe@c750fbf1b)
Visual Studio extension to enable Xamarin Designer tools in Visual Studio.

Xamarin Templates 16.10.5 (355b57a)
Templates for building iOS, Android, and Windows apps with Xamarin and Xamarin.Forms.

Xamarin.Android SDK 11.3.0.1 (d16-10/22fc2b3)
Xamarin.Android Reference Assemblies and MSBuild support.
Mono: b4a3858
Java.Interop: xamarin/java.interop/d16-10@f39db25
ProGuard: Guardsquare/proguard@912d149
SQLite: xamarin/sqlite@85460d3
Xamarin.Android Tools: xamarin/xamarin-android-tools/d16-10@c5732a0

Xamarin.iOS and Xamarin.Mac SDK 14.20.0.1 (fe0e2c518)
Xamarin.iOS and Xamarin.Mac Reference Assemblies and MSBuild support.

Screenshots

Reproduction Link

Sorry just happened in our production app.

Workaround

None yet. But imho if we could have a null checker here could solve the crash.