Can't build Xamarin.Android project in VS 2019 with SignAndroidPackage as default MSBuild target

[LDan1117]

Steps to Reproduce

1. Create a new Xamarin Android project in Visual Studio 2019 (v16.3.1 with Xamarin.Android.SDK 10.0.0.43 and Xamarin 16.0.3.274)
2. Build in Release|AnyCPU. The build is successful.
3. Edit the .csproj file and change the "DefaultTargets" to "SignAndroidPackage" instead of "Build".
4. Build in Release|AnyCPU. The build fails with the following error:

The "LinkAssemblies" task failed unexpectedly.
System.IO.FileNotFoundException: Could not load assembly 'SignAndroidPackageErrorSample, Version=0.0.0.0, Culture=neutral, PublicKeyToken='.
Perhaps it doesn't exist in the Mono for Android profile?
File name: 'SignAndroidPackageErrorSample.dll'
   at Java.Interop.Tools.Cecil.DirectoryAssemblyResolver.Resolve(AssemblyNameReference reference, ReaderParameters parameters)
   at Java.Interop.Tools.Cecil.DirectoryAssemblyResolver.GetAssembly(String fileName)
   at Xamarin.Android.Tasks.LinkAssemblies.Execute(DirectoryAssemblyResolver res)
   at Xamarin.Android.Tasks.LinkAssemblies.Execute()
   at Microsoft.Build.BackEnd.TaskExecutionHost.Microsoft.Build.BackEnd.ITaskExecutionHost.Execute()
   at Microsoft.Build.BackEnd.TaskBuilder.<ExecuteInstantiatedTask>d__26.MoveNext()

Expected Behavior

The build must not fail. An .apk file must be created and signed.

Actual Behavior

The build fails.

Version Information

Microsoft Visual Studio Enterprise 2019
Version 16.3.1
VisualStudio.16.Release/16.3.1+29324.140
Microsoft .NET Framework
Version 4.8.03761

Installed Version: Enterprise

Visual C++ 2019 00435-60000-00000-AA987
Microsoft Visual C++ 2019

C# Tools 3.3.1-beta3-19461-02+2fd12c210e22f7d6245805c60340f6a34af6875b
C# components used in the IDE. Depending on your project type and settings, a different version of the compiler may be used.

Mono Debugging for Visual Studio 16.3.7 (9d260c5)
Support for debugging Mono processes with Visual Studio.

NuGet Package Manager 5.3.0
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

Snapshot Debugging Extension 1.0
Snapshot Debugging Visual Studio Extension Detailed Info

VisualStudio.Mac 1.0
Mac Extension for Visual Studio

Xamarin 16.3.0.274 (d16-3@06531f8)
Visual Studio extension to enable development for Xamarin.iOS and Xamarin.Android.

Xamarin Designer 16.3.0.230 (remotes/origin/d16-3-xcode11@bbe518670)
Visual Studio extension to enable Xamarin Designer tools in Visual Studio.

Xamarin Templates 16.3.565 (27e9746)
Templates for building iOS, Android, and Windows apps with Xamarin and Xamarin.Forms.

Xamarin.Android SDK 10.0.0.43 (d16-3/8af1ca8)
Xamarin.Android Reference Assemblies and MSBuild support.
Mono: mono/mono@7af64d1ebe9
Java.Interop: xamarin/java.interop/d16-3@5836f58
LibZipSharp: grendello/LibZipSharp/d16-3@71f4a94
LibZip: nih-at/libzip@b95cf3f
ProGuard: xamarin/proguard@905836d
SQLite: xamarin/sqlite@8212a2d
Xamarin.Android Tools: xamarin/xamarin-android-tools/d16-3@cb41333

Xamarin.iOS and Xamarin.Mac SDK 13.2.0.42 (5e8a208)
Xamarin.iOS and Xamarin.Mac Reference Assemblies and MSBuild support.

Log File

The sample project, screenshots, and logs are attached.



SignAndroidPackageError.log
SignAndroidPackageErrorSample.zip

[LDan1117]

I've also noticed that the build is successful in VS 2017 (MSBuild 15) and Visual Studio for Mac (8.3.1 build 18). Thus the matter is probably with MSBuild 16.

[dellis1972]

We made some changes too SignAndroidPackage to speed up build times. It not longer depends on Build when building from inside the IDE. As a result Build is probably not being called now.

The IDE will call the Default target (normally build) and has internal state so it knows when it really needs to build again. When hitting the Run button in the IDE our tooling therefore only calls SignAndroidPackage and then Install. Since we know already if the Build was up to date there was no need for SignAndroidPackage to depend on it.

You can try changing DefaultTargets to Build;SignAndroidPackage if that is what you really need.
But be warned, this might break some of the build improvements we have been making and will probably slow down your build/deploy/debug times.

I don't think this is a bug since our system is working as designer. So I will close this for now, feel free to re-open the issue if the above workaround does not work.

[LDan1117]

Thank you, @dellis1972 !

I've added the Build target and this helped to get rid of the error. Though I'm wondering why I didn't witness the error on Mac?
Considering the changes were made to SignAndroidPackage target it must have appeared in VS for Mac as well, mustn't it?.

[dellis1972]

VSforMac has a different internal build process to that of VS on Windows. So they don't always behave in the same way. Allot of this depends on the BuildingInsideVisualStudio MSBuild flag, which VS on Windows sets to true, I suspect VSforMac is not setting that property at all. That means it will default to the command line behaviour which is to do a Build as part of the SignAndroidPackage call.

Skipping the Build dependency when hitting F5 in VS for Windows can save you a number of seconds on your dev loop when debugging. It takes time for MSBuild to figure out everything is up to date, even if you haven't made any changes.