Bug 35121 - Exception when running UWP release build (.NET Native)
Summary: Exception when running UWP release build (.NET Native)
Alias: None
Product: Forms
Classification: Xamarin
Component: Windows ()
Version: 1.5.1
Hardware: PC Windows
: --- normal
Target Milestone: UWP
Assignee: E.Z. Hart [MSFT]
Depends on:
Reported: 2015-10-20 20:04 UTC by Dominik Weber
Modified: 2015-11-11 18:28 UTC (History)
2 users (show)

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

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Description Dominik Weber 2015-10-20 20:04:44 UTC
When running a UWP app built with release configuration and .NET Native toolchain enabled an exception is thrown in Xamarin.Forms.Forms.Init(e).

System.IndexOutOfRangeException: Arg_IndexOutOfRangeException
   at Xamarin.Forms.Registrar.RegisterAll(Type[] attrTypes)
   at Xamarin.Forms.Forms.Init(LaunchActivatedEventArgs launchActivatedEventArgs)
   at App1.App.OnLaunched(LaunchActivatedEventArgs e) in C:\Users\Dominik\Documents\Salesperformer\joey\Clients\wunderapp\App1\App.xaml.cs:line 42
   at Xamarin.Forms.TriggerAction.DoInvoke(Object sender)
   at Windows.UI.Xaml.IApplicationOverrides__Impl.Vtbl.OnLaunched__STUB(IntPtr pComThis, Vtbl** unsafe_args) in c:\Users\Dominik\Documents\Salesperformer\joey\Clients\wunderapp\App1\obj\x86\Release\ilc\intermediate\App1.Interop\ImplTypes.g.cs:line 111718

Just create a new UWP app, add Xamarin.Forms and add the call to Forms.Init() to reproduce the problem. Build and run using x86 release configuration with .NET native enabled (is enabled by default).

I tried using both the current UWP preview release ( and the newest Forms release (
Comment 1 Dominik Weber 2015-10-20 20:11:22 UTC
The problem might originate from the implementation of WindowsBasePlatformServices.GetAssemblies:

This method searches the installation path for dll and exe files and loads them. With .Net native enabled only two main assemblies are created: <Appname>.exe and <Appname>.dll. (no Xamarin.Forms.dll etc)
The implementation of GetAssemblies tries to load them without the file extension, which unfortunately makes them indistinguishable.
Comment 2 E.Z. Hart [MSFT] 2015-11-11 18:28:38 UTC
Fixed in next UWP release