Bug 25016 - Intermittent Cross Thread Exception Quitting Xamarin Forms App on Windows Phone
Summary: Intermittent Cross Thread Exception Quitting Xamarin Forms App on Windows Phone
Alias: None
Product: Forms
Classification: Xamarin
Component: Forms ()
Version: 1.3.0
Hardware: PC Windows
: Normal normal
Target Milestone: ---
Assignee: Bugzilla
Depends on:
Reported: 2014-12-02 18:11 UTC by troywillmot
Modified: 2016-03-25 18:48 UTC (History)
4 users (show)

Is this bug a regression?: ---
Last known good build:

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Description troywillmot 2014-12-02 18:11:15 UTC
Sometimes when quitting a WP app built with Forms (using the back button), I get the following unhandled exception which seems to be from Xamarin and not my code. Note, I have used the Xamarin.Forms.Device.StartTimer method to start some 5 minutes timers earlier in the app. The timers are supposed to stop themselves at appropriate times, but because of the design pattern used by Xamarin for this API I can't explicitly stop them before quitting. These timers may relate to this error.

{System.UnauthorizedAccessException: Invalid cross-thread access.
   at MS.Internal.XcpImports.CheckThread()
   at MS.Internal.XcpImports.DispatcherTimer_Stop(DispatcherTimer timer)
   at System.Windows.Threading.DispatcherTimer.Stop()
   at Xamarin.Forms.WinPhoneTicker.DisableTimer()
   at Xamarin.Forms.Ticker.Disable()
   at Xamarin.Forms.Ticker.Remove(Int32 handle)
   at Xamarin.Forms.Tweener.Finalize()}
Comment 1 Ram Chandra 2015-01-07 11:40:55 UTC
I have checked this issue but I am unable to reproduce this behavior.

Steps I followed:

1. Create an Blank app( Xamarin.Forms Portable)
2. Add a new class to portable project(ClockViewModel)
3. Write the following code in ClockViewModel class.

    class ClockViewModel : INotifyPropertyChanged
        DateTime dateTime;

        public event PropertyChangedEventHandler PropertyChanged;

        public ClockViewModel()
            this.DateTime = DateTime.Now;

            Device.StartTimer(TimeSpan.FromSeconds(1), () =>
                    this.DateTime = DateTime.Now;
                    return true;

        public DateTime DateTime
                if (dateTime != value)
                    dateTime = value;

                    if (PropertyChanged != null)
                            new PropertyChangedEventArgs("DateTime"));
                return dateTime;

4. Add a new Xaml page to Portable project (name=ClockView).
5. Write the following code in newly added xaml page.
   <ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
             Title="Clock View">
  <Label Text="{Binding DateTime,StringFormat='{0:T}'}" Font="Large" HorizontalOptions="Center" VerticalOptions="Center">
      <local:ClockViewModel />

6. In App.cs file navigate to ClockView page.
7. Build and deploy application to device/emulator.
8. Press the back button of device.

When I deploy the project to the and press the back button I observed that I am not getting any error or exception and my application is working fine.

Screencast: http://www.screencast.com/t/Jl3cRxQgFuJz

Could you please provide sample application, build info (Xamarin for VS + Xamarin.Forms) and logs (IDE + build logs)? So that we can reproduce this issue at our end. 

You can get build info from here:
Visual Studio => Help => About Microsoft Visual Studio => Copy Info

You can get debug logs from here :
Visual Studio => Debug => Window => Output => select debug option from drop down and attach the logs.

You can get IDE logs from here:
Visual Studio => Help => Zip Xamarin Logs

Environment Info:

Xamain.Forms :

Microsoft Visual Studio Professional 2013
Version 12.0.30723.00 Update 3
Microsoft .NET Framework
Version 4.5.51641

Installed Version: Professional

LightSwitch for Visual Studio 2013   06177-004-0447006-02641
Microsoft LightSwitch for Visual Studio 2013

Team Explorer for Visual Studio 2013   06177-004-0447006-02641
Microsoft Team Explorer for Visual Studio 2013

Visual Basic 2013   06177-004-0447006-02641
Microsoft Visual Basic 2013

Visual C# 2013   06177-004-0447006-02641
Microsoft Visual C# 2013

Visual C++ 2013   06177-004-0447006-02641
Microsoft Visual C++ 2013

Visual F# 2013   06177-004-0447006-02641
Microsoft Visual F# 2013

Visual Studio 2013 Code Analysis Spell Checker   06177-004-0447006-02641
Microsoft® Visual Studio® 2013 Code Analysis Spell Checker

Portions of International CorrectSpell™ spelling correction system © 1993 by Lernout & Hauspie Speech Products N.V. All rights reserved.

The American Heritage® Dictionary of the English Language, Third Edition Copyright © 1992 Houghton Mifflin Company. Electronic version licensed from Lernout & Hauspie Speech Products N.V. All rights reserved.

Windows Phone SDK 8.0 - ENU   06177-004-0447006-02641
Windows Phone SDK 8.0 - ENU

Application Insights Tools for Visual Studio Package   1.0
Application Insights Tools for Visual Studio

ASP.NET and Web Tools   12.3.50717.0
Microsoft Web Developer Tools contains the following components:
Support for creating and opening ASP.NET web projects
Browser Link: A communication channel between Visual Studio and browsers
Editor extensions for HTML, CSS, and JavaScript
Page Inspector: Inspection tool for ASP.NET web projects
Scaffolding: A framework for building and running code generators
Server Explorer extensions for Microsoft Azure Websites
Web publishing: Extensions for publishing ASP.NET web projects to hosting providers, on-premises servers, or Microsoft Azure

ASP.NET Web Frameworks and Tools 2012.2   4.1.21001.0
For additional information, visit http://go.microsoft.com/fwlink/?LinkID=309563

ASP.NET Web Frameworks and Tools 2013   5.2.20703.0
For additional information, visit http://www.asp.net/

Common Azure Tools   1.2
Provides common services for use by Azure Mobile Services and Microsoft Azure Tools.

Microsoft Advertising SDK for Windows Phone   
Microsoft Advertising SDK for Windows Phone

Microsoft Azure Mobile Services Tools   1.2
Microsoft Azure Mobile Services Tools

NuGet Package Manager   2.8.50926.663
NuGet Package Manager in Visual Studio. For more information about NuGet, visit http://docs.nuget.org/.

Office Developer Tools for Visual Studio 2013 ENU   12.0.30626
Microsoft Office Developer Tools for Visual Studio 2013 ENU

PowerShell Tools   1.2
Provides file classification services using PowerShell

PreEmptive Analytics Visualizer   1.2
Microsoft Visual Studio extension to visualize aggregated summaries from the PreEmptive Analytics product.

SQL Server Data Tools   12.0.30919.1
Microsoft SQL Server Data Tools

Windows Phone 8.1 SDK Integration   1.0
This package integrates the tools for the Windows Phone 8.1 SDK into the menus and controls of Visual Studio.

Workflow Manager Tools 1.0   1.0
This package contains the necessary Visual Studio integration components for Workflow Manager.

Xamarin (10cfd178d55287f09c85f5a1e604dfe20889a40f)
Visual Studio extension to enable development for Xamarin.iOS and Xamarin.Android.

Xamarin.Android (ba9bbbdd44cfdc4bf485e8885bd2ad24fba525f7)
Visual Studio plugin to enable development for Xamarin.Android.

Xamarin.iOS (840a925103a0bf4a856507f13d5eaee3c1579c2f)
Visual Studio extension to enable development for Xamarin.iOS.

Xamarin.iOS Unified Migration   1.0
Automated migration for Xamarin iOS Classic projects to Unified
Comment 2 Jason Smith [MSFT] 2016-03-25 18:48:49 UTC
Thank you for taking the time to submit this report. After reviewing the description of this bug, we no longer believe it affects the current version of Xamarin.Forms. If you are still experiencing the issue after updating your packages, please reopen this report with an attached reproduction.
For your convenience, we have created some reproduction best practices viewable here: https://gist.github.com/jassmith/92405c300e54a01dcc6d

Warm regards,
Xamarin Forms Team