Can't get past `javac: error: package androidx.fragment.app does not exist` about androidx

[jpobst]

I suspect using <Reference> is the issue. These .dlls do not contain the .aar embedded in them for build performance reasons.

When you reference it as a <PackageReference> the MSBuild system will run any .targets files in the NuGet package when you build your project.

If you look in the NuGet you'll see build\monoandroid12.0\Xamarin.AndroidX.Fragment.targets.

This contains this MSBuild which adds the .aar to your project:

<ItemGroup>
  <AndroidAarLibrary Include="$(MSBuildThisFileDirectory)..\..\aar\androidx.fragment.fragment.aar">
    <AndroidXSkipAndroidXMigration>true</AndroidXSkipAndroidXMigration>
  </AndroidAarLibrary>
</ItemGroup>

By using a <Reference> instead of a <PackageReference> this never gets executed and the .aar never gets added to your application.

[justin-caldicott]

Many thanks @jpobst, all set!

I'm not in a position to switch to <PackageReference> just yet. But what you explained let me realise I could just add the android library references to the project file directly. They probably would have been added if I'd installed the package properly, rather than just installing them to a folder. Really do need to update our build scripts!

So I have a bunch of additional lines like:

    <AndroidAarLibrary Include="$(ProjectDir)..\packages\Xamarin.AndroidX.Fragment\aar\androidx.fragment.fragment.aar"/>

There were already a couple there for Kotlin.StdLib and Kotlin.StdLib.Common.

Sorry, not really an issue in the product then, just support.. but much appreciated. Closing.

[jpobst]

Have you added the following NuGet packages to your project?

• Xamarin.AndroidX.Fragment
• Xamarin.AndroidX.Core

[justin-caldicott]

Thanks @jpobst, yes I added the new packages and followed the errors in Rider to make sure all implicit dependencies are included too. There are no C# errors now, just these java ones.

I admit I'm not sure how the java side of the bindings work. The java files with errors are in e.g. obj/Debug/android/<guid>/SomeFragment.java. The lines it's complaining about are:

public class SomeFragment
	extends androidx.fragment.app.Fragment <<<<<< javac cannot find androidx.fragment.app
	implements
		mono.android.IGCUserPeer

I saw in the installed packages there's an aar folder with e.g. androidx.fragment.fragment.aar inside. Presumably this is where it should be finding the package from?

One unusual thing here is we restore packages with -ExcludeVersion to a packages folder within the repo root. Assembly resolution is OK with this due to hint paths, e.g.

    <Reference Include="Xamarin.AndroidX.Fragment">
      <HintPath>..\packages\Xamarin.AndroidX.Fragment\lib\monoandroid12.0\Xamarin.AndroidX.Fragment.dll</HintPath>
    </Reference>

Maybe this causes problems for java package resolution somehow? It didn't have this behaviour on previous versions, but then we're jumping a lot of versions in one go as the app wasn't updated for a couple of years.