Solution that crashes on startup when aapt2 is used

[jonathanpeppers]

Related to:

• [Bug] Xamarin.Forms 4 (4.0.0.425677) fails Image in Button when resources are defined in Android class library xamarin/Xamarin.Forms#6327
• [Bug] Xamarin.Forms 3.6 and Xamarin.Forms.Visual.Material 3.6 failed with exception when resources are defined in Android class library xamarin/Xamarin.Forms#6343

Steps to Reproduce

1. Clone: https://github.com/zijianhuang/xamarinforms4bugs/tree/ResourcesInLib (use the ResourcesInLib branch)
2. Build/Deploy with 16.2/master
3. App crashes on start with:

06-04 15:47:55.260 25714 25714 I MonoDroid: Java.Lang.NoClassDefFoundError: Failed resolution of: Landroid/support/v7/appcompat/R$drawable; ---> Java.Lang.ClassNotFoundException: Didn't find class "android.support.v7.appcompat.R$drawable" on path: DexPathList[[zip file "/system/framework/org.apache.http.legacy.boot.jar", zip file "/data/app/com.companyname.Demo2.Android-PozTNMz4ZBMXaHx-doetdQ==/base.apk"],nativeLibraryDirectories=[/data/app/com.companyname.Demo2.Android-PozTNMz4ZBMXaHx-doetdQ==/lib/arm64, /data/app/com.companyname.Demo2.Android-PozTNMz4ZBMXaHx-doetdQ==/base.apk!/lib/arm64-v8a, /system/lib64]]
06-04 15:47:55.260 25714 25714 I MonoDroid:    --- End of inner exception stack trace ---
06-04 15:47:55.260 25714 25714 I MonoDroid:   at Java.Interop.JniEnvironment+InstanceMethods.CallNonvirtualVoidMethod (Java.Interop.JniObjectReference instance, Java.Interop.JniObjectReference type, Java.Interop.JniMethodInfo method, Java.Interop.JniArgumentValue* args) [0x00089] in <372c976a2c5d45cb9abb001729e14dbf>:0
06-04 15:47:55.260 25714 25714 I MonoDroid:   at Java.Interop.JniPeerMembers+JniInstanceMethods.InvokeVirtualVoidMethod (System.String encodedMember, Java.Interop.IJavaPeerable self, Java.Interop.JniArgumentValue* parameters) [0x0005d] in <372c976a2c5d45cb9abb001729e14dbf>:0
06-04 15:47:55.260 25714 25714 I MonoDroid:   at Android.App.Activity.OnCreate (Android.OS.Bundle savedInstanceState) [0x00031] in <547679cba0d64c03859bc6ab9919a165>:0
06-04 15:47:55.260 25714 25714 I MonoDroid:   at Xamarin.Forms.Platform.Android.FormsAppCompatActivity.OnCreate (Android.OS.Bundle savedInstanceState) [0x0001d] in <02288cf327c341c79f8385d5db4c09bf>:0
06-04 15:47:55.260 25714 25714 I MonoDroid:   at Demo2.Droid.MainActivity.OnCreate (Android.OS.Bundle savedInstanceState) [0x00001] in <16681ab0b39d4abe8efd53e748c930e4>:0
06-04 15:47:55.260 25714 25714 I MonoDroid:   at Android.App.Activity.n_OnCreate_Landroid_os_Bundle_ (System.IntPtr jnienv, System.IntPtr native__this, System.IntPtr native_savedInstanceState) [0x00011] in <547679cba0d64c03859bc6ab9919a165>:0
06-04 15:47:55.260 25714 25714 I MonoDroid:   at (wrapper dynamic-method) Android.Runtime.DynamicMethodNameCounter.7(intptr,intptr,intptr)
06-04 15:47:55.260 25714 25714 I MonoDroid:   --- End of managed Java.Lang.NoClassDefFoundError stack trace ---

The obj\Debug\81\android\src\android\support\v7\appcompat\R.java file did not exist.

If I build with /p:AndroidUseAapt2=False, then everything works correctly.

This solution is setup in an odd way:

• Demo2.csproj - forms netstandard stuff
• Demo2.Android.csproj - android head project, note that @(AndroidResource) is empty
• ClassLibrary1.Android.csproj - android class library with all the resources

Somehow both <Aapt/> and <Aapt2Link/> are skipped here, causing the issue:

Expected Behavior

Even though this project is setup in an odd way, it should work with aapt2 enabled.

Actual Behavior

This solution crashes on startup with aapt2 enabled.

Version Information

16.2/master

Log File

Logs.zip

[jonathanpeppers]

The root cause might be:

Target Name=_CompileResources Project=Demo2.Android.csproj
    ...
    Skipping target "_CompileResources" because it has no inputs.
    Though the target has declared its inputs, the input specification only references empty properties and/or empty item lists.

Because @(AndroidResource) is empty in the head project.

[jonathanpeppers]

I think the fix might be as simple as this:

diff --git a/src/Xamarin.Android.Build.Tasks/Xamarin.Android.Common.targets b/src/Xamarin.Android.Build.Tasks/Xamarin.Android.Common.targets
index 94f6851a..3fd5b932 100755
--- a/src/Xamarin.Android.Build.Tasks/Xamarin.Android.Common.targets
+++ b/src/Xamarin.Android.Build.Tasks/Xamarin.Android.Common.targets
@@ -1699,7 +1699,7 @@ because xbuild doesn't support framework reference assemblies.
        />

        <Aapt2Link
-               Condition="'$(_AndroidResourceDesignerFile)' != '' And '$(_AndroidUseAapt2)' == 'True' And Exists ('$(_AndroidLibraryFlatArchivesDirectory)\compiled.flata')"
+               Condition="'$(_AndroidResourceDesignerFile)' != '' And '$(_AndroidUseAapt2)' == 'True'"
                ContinueOnError="$(DesignTimeBuild)"
                ResourceNameCaseMap="$(_AndroidResourceNameCaseMap)"
                AssemblyIdentityMapFile="$(_AndroidLibrayProjectAssemblyMapFile)"

Tomorrow, I'll see if I can get a PR. I'll need to come up with a test showing this problem.