Information on Xamarin.Android

By Edward Brey and Ronan Burke

This page shows how to automate Obfuscar for Xamarin.Android using MSBuild. Integration for other Xamarin platforms is similar.

Nuget Package

Install the Obfuscar NuGet package into the Xamarin.Android project.

Install-Package Obfuscar

Project File

In the Xamarin.Android project file (.csproj), add an AfterBuild target to run the obfuscator.

The obfuscator runs from MonoAndroidIntermediateAssetsDir, which is the assets directory that gets bundled into the APK. An example of this directory is obj\Release\90\android\assets.

The obfuscator outputs to the target directory (e.g. bin\Release) so that the mapping file will go there. It then copies the obfuscated files to the assets directory.

This is an example target for obfuscating a single assembly called MyAssembly.dll:

<Target Name="AfterBuild" Condition=" '$(Configuration)' == 'Release' ">
  <Exec WorkingDirectory="$(MonoAndroidIntermediateAssetsDir)" Command="$(Obfuscar) $(ProjectDir)obfuscar.xml" />
  <Copy SourceFiles="$(TargetDir)MyAssembly.dll" DestinationFolder="$(MonoAndroidIntermediateAssetsDir)" />
</Target>

It is a good idea to place this near the bottom of your project file after all other targets to ensure it is run.

Obfuscar Configuration File

Create obfuscar.xml in the Xamarin.Android project. Configure it to output to the target directory relative to the assets directory.

<Obfuscator>
  <Var name="OutPath" value="..\..\..\..\..\bin\Release" />
  <Module file="MyAssembly.dll" />
</Obfuscator>

Troubleshooting

To more effectively troubleshoot issues, you can use the following tools/methods:

  • Temporarily change the AfterBuild target mentioned above to be for the ‘Debug’ configuration. Add a debug message to the configuration so you can confirm the task is being run:

<Target Name="AfterBuild" Condition=" '$(Configuration)' == 'Debug' ">
  <Message Importance="High" Text="Obfuscar task has been called." />
  <Exec WorkingDirectory="$(MonoAndroidIntermediateAssetsDir)" Command="$(Obfuscar) $(ProjectDir)obfuscar.xml" />
  <Copy SourceFiles="$(TargetDir)MyAssembly.dll" DestinationFolder="$(MonoAndroidIntermediateAssetsDir)" />
</Target>

Update obfuscar.xml to output to the Debug folder:

<Var name="OutPath" value="..\..\..\..\..\bin\Debug" />

  • Run your application in Debug mode. In Visual Studio, go to Debug > Windows > Exception Settings. Enable Common Language Runtime Exceptions. When your app runs, this will allow you to see if you are getting any new exceptions when obfuscation is enabled.

  • If your app crashes on startup with no obvious exceptions, go to Tools > Android > Device Log... and use the messages from Logcat to diagnose/research the errors you get.

Linking issues

With linking enabled, you may get this error message:

XALNK7000: Java.Interop.Tools.Diagnostics.XamarinAndroidException: error XA2006: Could not resolve reference to ' . '
...
When the scope is different from the defining assembly, it usually means that the type is forwarded. ---> Mono.Cecil.ResolutionException: Failed to resolve  .

With linking disabled, you may get this error message:

JAVAC0000:  error: illegal character: '\u2006' xamarin forms

The above two errors can be resolved by using this property in obfuscar.xml:

<Var name="UseUnicodeNames" value="false" />

AndroidX issues

Using Obfuscar can reveal issues with an improper AndroidX migration in Xamarin. If you get an error like this:

System.InvalidCastException: Unable to convert instance of type 'Google.Android.Material.Internal.CheckableImageButton' to type 'AndroidX.AppCompat.Widget.Toolbar'

You should update “android.support.v7.widget.Toolbar” to “androidx.appcompat.widget.Toolbar” in Toolbar.xml. You should rename the file to Toolbar.axml. You should update “android.support.design.widget.TabLayout” to “com.google.android.material.tabs.TabLayout” in Tabbar.xml. You should rename the file to Tabbar.axml.

The Xamarin.Forms team recommend removing these files altogether , but you may encounter other issues when running your Android app after doing this.

Dependency injection errors

If you are using dependency injection and are getting dependency injection errors, ensure public items are kept in obfuscar.xml:

<Var name="KeepPublicApi" value="true" />