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Created attachment 23577 [details]
Example project that shows the issue
[Video, with a walkthrough showing the bug in action]: https://vimeo.com/225633853/bf3b02d0f6
I have the following code in my ViewModel.
public LoginViewModel(IAuthModel model) :
_model = model;
public IRelayCommand LoginCommand
return GetCommand(() =>
return Execution.ViewModelExecute(new LoginOperation(_model));
Now, I thought that before any 'get' can be performed on the LoginCommand, it must complete the constructor first. This runs as expected on UWP, constructor first, then 'get'. But on Android, it runs the 'get' in the property first, then the constructor.
Now to go even stranger, if I then go into the GetCommand method, and put a return if the Execution property is null in there, as so.
public IRelayCommand GetCommand(Func<IRelayCommand> create, [CallerMemberName] string name = "")
// This is what i just added in
if (Execution == null)
// This is the existing code.
Then the constructor always runs first, then the 'get' in the property. If I comment out those first 2 lines, it reverts back to it's previous way of running the 'get' before constructor. Am I missing something, or is this a strange bug? I am thinking a compiler optimization issue.
Attached is the project where this issue occurs.
Below is my Visual Studio setup.
Microsoft Visual Studio Enterprise 2017
Version 15.2 (26430.15) Release
Microsoft .NET Framework
Installed Version: Enterprise
Architecture Diagrams and Analysis Tools 00369-90252-65973-AA415
Microsoft Architecture Diagrams and Analysis Tools
Visual Basic 2017 00369-90252-65973-AA415
Microsoft Visual Basic 2017
Visual C# 2017 00369-90252-65973-AA415
Microsoft Visual C# 2017
Visual C++ 2017 00369-90252-65973-AA415
Microsoft Visual C++ 2017
Visual F# 4.1 00369-90252-65973-AA415
Microsoft Visual F# 4.1
Application Insights Tools for Visual Studio Package 8.6.00404.2
Application Insights Tools for Visual Studio
ASP.NET and Web Tools 2017 15.0.30503.0
ASP.NET and Web Tools 2017
ASP.NET Web Frameworks and Tools 2017 5.2.50303.0
For additional information, visit https://www.asp.net/
Azure App Service Tools v3.0.0 15.0.30209.0
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 2.2.5000.0
Microsoft Azure Data Lake Tools for Visual Studio
Common Azure Tools 1.9
Provides common services for use by Azure Mobile Services and Microsoft Azure Tools.
Fabric Diagnostic Events
A Visual Studio Extension that brings the GitHub Flow into Visual Studio.
KofePackagePackage Extension 1.0
KofePackagePackage Visual Studio Extension Detailed Info
Merq 1.1.17-rc (cba4571)
Command Bus, Event Stream and Async Manager for Visual Studio extensions.
Microsoft Azure Hive Query Language Service 2.2.5000.0
Language service for Hive query
Microsoft Azure Tools 2.9
Microsoft Azure Tools for Microsoft Visual Studio 2017 - v2.9.50131.1
Microsoft MI-Based Debugger 1.0
Provides support for connecting Visual Studio to MI compatible debuggers
Microsoft Visual Studio VC Package 1.0
Microsoft Visual Studio VC Package
Mono Debugging for Visual Studio Mono.Debugging.VisualStudio
Support for debugging Mono processes with Visual Studio.
NuGet Package Manager 4.2.0
NuGet Package Manager in Visual Studio. For more information about NuGet, visit http://docs.nuget.org/.
SQL Server Data Tools 15.1.61702.140
Microsoft SQL Server Data Tools
Hosting json editor into a tool window
TypeScript tools for Visual Studio
Visual C++ for Cross Platform Mobile Development (Android) 15.0.26228.00
Visual C++ for Cross Platform Mobile Development (Android)
Visual Studio Tools for Universal Windows Apps 15.0.26430.06
The Visual Studio Tools for Universal Windows apps allow you to build a single universal app experience that can reach every device running Windows 10: phone, tablet, PC, and more. It includes the Microsoft Windows 10 Software Development Kit.
Xamarin 22.214.171.1246 (fec6f88)
Visual Studio extension to enable development for Xamarin.iOS and Xamarin.Android.
Xamarin.Android SDK 126.96.36.199 (9dbc4c5)
Xamarin.Android Reference Assemblies and MSBuild support.
Xamarin.iOS and Xamarin.Mac SDK 10.10.0.37 (ad35de4)
Xamarin.iOS and Xamarin.Mac Reference Assemblies and MSBuild support.
Thank you for the report. I attempted to reproduce this behavior with your default project (Not modifying any workarounds), I run into the expected behavior when debugging. That is of course hitting the CTOR and then the get.
Some other details that might be helpful:
What API are you deploying to? I tried 19, 21, 24 for some quick tests.
Is this 100% reproducible? Have you tried multiple devices/emulators and the API combinations between the two?
Seeing that I'm on the same build as you, this seems to be a little more specific to something else. Can you let me know via a few tests if we can figure out what the odd thing out is?
I just did some more testing and yes, I can continue to reproduce it, 100% of the time. The Video link I attached to the original report, showing it in action, is exactly what is happening.
I am deploying on Min API 16 and Compiling against API 25. I did also try API 24 and 23, then changing the Min to 21.
I have tried on the emulator (Android 6.0 x86) and I have tried on a real device (Sony Xperia F3115, Android 7.0).
This occurs in both Debug and Release mode.
The GetCommand will always run before the CTOR, unless I put in
if (Execution == null)
I am currently building with no AOT, no Shared Runtime, no ProGuard, no linking.
Happy to try out anything more, if you have any suggestions. My local PC is an Intel i7-7700HQ Kaby Lake, if that might have anything to do with it.
Forgot to change status back to NEW
(In reply to Adam from comment #2)
> Hi Jon
> I just did some more testing and yes, I can continue to reproduce it, 100%
> of the time. The Video link I attached to the original report, showing it in
> action, is exactly what is happening.
> I am deploying on Min API 16 and Compiling against API 25. I did also try
> API 24 and 23, then changing the Min to 21.
> I have tried on the emulator (Android 6.0 x86) and I have tried on a real
> device (Sony Xperia F3115, Android 7.0).
> This occurs in both Debug and Release mode.
> The GetCommand will always run before the CTOR, unless I put in
> if (Execution == null)
> return null;
> I am currently building with no AOT, no Shared Runtime, no ProGuard, no
> Happy to try out anything more, if you have any suggestions. My local PC is
> an Intel i7-7700HQ Kaby Lake, if that might have anything to do with it.
I had attempted this on three physiacal different devices(API 23, 24, 25) using 15.2. I also tried a few x86 emulators (24-25) The behavior remains what you would "Expect" on each device which is the constructor being executed prior to the get call.
15.3 (Preview 7.0) isn't really testable as it shows:
Checking compatibility for Xamarin.Forms 188.8.131.52-pre5 with .NETStandard,Version=v1.3.
NU1202: Package Xamarin.Forms 184.108.40.206-pre5 is not compatible with netstandard1.3 (.NETStandard,Version=v1.3). Package Xamarin.Forms 220.127.116.11-pre5 supports:
- monoandroid10 (MonoAndroid,Version=v1.0)
- portable-monoandroid10+net45+win+win81+wp8+wpa81+xamarinios10+xamarinmac20 (.NETPortable,Version=v0.0,Profile=win+net45+wp80+win81+wpa81+MonoAndroid10+Xamarin.iOS10+xamarinmac20)
- uap10.0 (UAP,Version=v10.0)
- win81 (Windows,Version=v8.1)
- wp8 (WindowsPhone,Version=v8.0)
- wpa81 (WindowsPhoneApp,Version=v8.1)
- xamarinios10 (Xamarin.iOS,Version=v1.0)
Perhaps a need to upgrade to .netstandard 1.0 supported package:
Intel(R) Core(TM) i7-6700K CPU @ 4.00GHz, 4001 Mhz, 4 Core(s), 8 Logical Processor(s)
Unfortunately I do not have a Kaby Lake. I will however ask a few colleagues to test this.
Could you attach a stack-trace from what you see as wrong get invocation
I should have checked the call stack before. Sorry guys, my bad. Perfect storm of oversights on my part. Reflection happening in my base class constructor, picking up the properties, and that wasn't in the sample I uploaded.
Again, really sorry for the wild goose chase, I feel really bad for wasting your time.