Java Callable Wrappers under Native AOT no longer forward C# attributes to Java annotations

[jonpryor]

Android framework version

net11.0-android (Preview)

Affected platform version

.NET 11 Preview 7

Description

dotnet/android has long supported forwarding C# custom attributes to Java annotations within generated Java Callable Wrappers. This also worked when targeting (experimental!) Native AOT:

# net 10!
dotnet new android -n android-jsiface
cd android-jsiface
cat <<'EOF' | git apply
diff --git a/MyWebViewHandler.cs b/MyWebViewHandler.cs
new file mode 100644
index 0000000..a3061b9
--- /dev/null
+++ b/MyWebViewHandler.cs
@@ -0,0 +1,10 @@
+using Android.Webkit;
+
+namespace impl;
+
+public class MyWebViewHandler : Example.WebViewHandlerBase {
+ [JavascriptInterface]
+ public override void PostMessage(string? message)
+ {
+ }
+}
diff --git a/WebViewHandlerBase.java b/WebViewHandlerBase.java
new file mode 100644
index 0000000..a249256
--- /dev/null
+++ b/WebViewHandlerBase.java
@@ -0,0 +1,4 @@
+package example;
+public abstract class WebViewHandlerBase {
+	public abstract void postMessage(String message);
+}
EOF
dotnet publish -r android-arm64 -p:PublishAot=true

The above would produce obj/Release/net10.0-android/android-arm64/android/src/crc64560613145aa5a4d6/MyWebViewHandler.java, which contained:

@android.webkit.JavascriptInterface
	public void postMessage (java.lang.String p0)
	{
		n_postMessage (p0);
	}

The C# [JavascriptInterface] custom attribute became the Java @JavascriptInterface annotation.

See: android-jsiface.zip

This worked through .NET 11 Preview 6.

Enter .NET 11 Preview 7, which introduces a modified Java Callable Wrapper generator with scrc64… package names for Native AOT; see 3f54298 and others.

.NEt 11 Preview 7 broke Native AOT support out of the box, but we can work around that by using Directory.Build.targets:

cat <<'EOF' | git apply
diff --git a/Directory.Build.targets b/Directory.Build.targets
new file mode 100644
index 0000000..4af58f5
--- /dev/null
+++ b/Directory.Build.targets
@@ -0,0 +1,14 @@
+<Project>
+	<!--
+	 Android+NativeAOT fails with .NET 11 Preview 7 with error NU1102:
+	 Unable to find package Microsoft.NETCore.App.Runtime.NativeAOT.android-arm64 with version (= 11.0.0-preview.7.26378.119)
+	 …because there is no published 11.0.0-preview.7.26378.119 package; it should be 11.0.0-preview.7.26381.103.
+
+	 This is the upstream fix: https://github.com/dotnet/android/pull/12356
+
+	 For now, Update `$(MicrosoftNETCoreAppRefPackageVersion)` to the correct version so that NuGet versions are correct.
+	 -->
+	<PropertyGroup Condition=" '$(BundledNETCoreAppPackageVersion)' == '11.0.0-preview.7.26381.103' ">
+		<MicrosoftNETCoreAppRefPackageVersion>11.0.0-preview.7.26381.103</MicrosoftNETCoreAppRefPackageVersion>
+	</PropertyGroup>
+</Project>
EOF

Next, update $(TargetFramework) to target net11.0-android:

cat <<'EOF' | git apply
diff --git a/android-jsiface.csproj b/android-jsiface.csproj
index 974a617..7834ed0 100644
--- a/android-jsiface.csproj
+++ b/android-jsiface.csproj
@@ -1,6 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
 <PropertyGroup>
- <TargetFramework>net10.0-android</TargetFramework>
+ <TargetFramework>net11.0-android</TargetFramework>
 <SupportedOSPlatformVersion>24</SupportedOSPlatformVersion>
 <RootNamespace>android_jsiface</RootNamespace>
 <OutputType>Exe</OutputType>
EOF

Resulting project: android-jsiface+net11.zip

Build for Native AOT using .NET 11 Preview 7:

dotnet publish -r android-arm64 -p:PublishAot=true

Now, investigate the Java Callable Wrapper for MyWebViewHandler, in obj/Release/net11.0-android/android-arm64/typemap/java/scrc64ea0c4e731f7fd0e6/MyWebViewHandler.java (note the /scrc64…, not /crc64…, which contains:

	@Override
	public void postMessage (java.lang.String p0)
	{
		n_PostMessage_Ljava_lang_String_ (p0);
	}

Note that @android.webkit.JavascriptInterface is not present.

---

Why does this matter? It breaks JavaScript bridging under Native AOT, which in turn means Uno unit tests fail, e.g. When_WebMessageReceived() (which is a timeout, and not really meaningful to anyone), but the cause is the missing @JavascriptInterface annotation within the Java Callable Wrapper.

Steps to Reproduce

Did you find any workaround?

No.

Relevant log output

[jonpryor]

On Discord, @jonathanpeppers mentioned a possible workaround: set $(_AndroidTypeMapImplementation)=llvm-ir. This will apparently become the $(AndroidTypeMapImplementation) MSBuild property in .NET 11 RC1.