Sample [to remove after moving into a unit test]

Use `@(AndroidJavaSource)` to add a pair of Java types:

    public class RemapActivity extends Activity {
        public void onMyCreate (android.os.Bundle bundle);
    }
    class ViewHelper {
        public static void mySetOnClickListener (android.view.View view, android.view.View.OnClickListener listener);
    }

Update `remap.xml` to:

 1. Rename `android.app.Activity` to `example.RemapActivity`
 2. Rename "`Activity.onCreate()`" to `RemapActivity.onMyCreate()`
 3. "Patch" `View.setOnClickListener()` to instead call
    `ViewHelper.mySetOnClickListener()`.

"Learnings" from this exercise:

 1. Changing the Java hierarchy "requires" changing the managed
    hierarchy to mirror it.

    If we rename `Activity` to `RemapActivity` but *don't* change
    `MainActivity` to inherit the (bound!) `Example.RemapActivity`,
    the app *crashes*:

        JNI DETECTED ERROR IN APPLICATION: can't call void example.RemapActivity.onMyCreate(android.os.Bundle) on instance of example.MainActivity

    This can be "fixed" *without* changing the base class
    of `MainActivity` by instead changing the base class of the
    Java Callable Wrapper for `MainActivity` to `example.RemapActivity`.
    This can be done manually, but isn't really supported in "normal"
    xamarin-android usage.

    Presumably InTune would make this Just Work by e.g. patching the
    `MainActivity.class` file.

 2. Note the "scare quotes" in (2): you *don't* rename
    `Activity.onCreate()`, because after renaming `Activity` to
    `example.RemapActivity`, `Activity` *no longer exists*.
    This warps the brain a bit.
    You can rename methods, but the `/replace-method/@source-type`
    value needs to be the `/replace-type/@to` value.

    This:

        <replace-method
            source-type="example/RemapActivity"
            source-method-name="onCreate"
            target-type="example/RemapActivity"
            target-method-name="onMyCreate" target-method-instance-to-static="false" />

    not this:

        <replace-method
            source-type="android/app/Activity"
            source-method-name="onCreate"
            target-type="example/RemapActivity"
            target-method-name="onMyCreate" target-method-instance-to-static="false" />

    While it would be more intuitive to support the latter,
    I couldn't figure out how to make it work robustly
    and efficiently.

 3. Don't intermix type renames with
    `/replace-method]@target-method-instance-to-static='true']`.
    It *can* be done, but also warps the brain.

    The deal with `@target-method-instance-to-static` is that it
    it changes the target method signature -- unless explicitly
    provided in `/replace-method/@target-method-signature` --
    so that the "source declaring type" is a prefix.

    Thus given

        <replace-method
            source-type="android/view/View"
            source-method-name="setOnClickListener"
            target-type="example/ViewHelper"
            target-method-name="mySetOnClickListener" target-method-instance-to-static="true" />

    we'll look for `ViewHelper.mySetOnClickListener(View, View.OnClickListener)`.

    If we renamed `View` to `MyView`, we would instead look for
    `ViewHelper.mySetOnClickListener(MyView, View.OnClickListener)`
    (note changed parameter type).

    This almost certainly *won't* work right for many circumstances.

Author: jonpryor

external/Java.Interop

@@ -9,7 +9,12 @@ namespace HelloWorld
 		Label           = "HelloWorld",
 		MainLauncher    = true,
 		Name            = "example.MainActivity")]
-	public class MainActivity : Activity
+	public class MainActivity :
+#if NET
+		Example.RemapActivity
+#else   // NET
+		Activity
+#endif  // NET
 	{
 		int count = 1;
 

samples/HelloWorld/HelloWorld/MainActivity.cs

@@ -0,0 +1,17 @@
+package example;
+
+import android.util.Log;
+
+public class RemapActivity extends android.app.Activity {
+    public void onMyCreate (android.os.Bundle bundle) {
+        Log.d ("*jonp*", "RemapActivity.onMyCreate() invoked!");
+        super.onCreate(bundle);
+    }
+}
+
+class ViewHelper {
+    public static void mySetOnClickListener (android.view.View view, android.view.View.OnClickListener listener) {
+        Log.d ("*jonp*", "ViewHelper.mySetOnClickListener() invoked!");
+        view.setOnClickListener (listener);
+    }
+}

samples/HelloWorld/HelloWorld/RemapActivity.java

@@ -1,3 +1,13 @@
 <replacements>
-  <replace-type from="android/app/Activity" to="android/app/ListActivity" />
+  <replace-type from="android/app/Activity" to="example/RemapActivity" />
+  <replace-method
+      source-type="example/RemapActivity"
+      source-method-name="onCreate"
+      target-type="example/RemapActivity"
+      target-method-name="onMyCreate" target-method-instance-to-static="false" />
+  <replace-method
+      source-type="android/view/View"
+      source-method-name="setOnClickListener"
+      target-type="example/ViewHelper"
+      target-method-name="mySetOnClickListener" target-method-instance-to-static="true" />
 </replacements>

samples/HelloWorld/HelloWorld/remap.xml

@@ -341,16 +341,25 @@ protected override IEnumerable<string> GetSimpleReferences (Type type)
 
 			Logger.Log (LogLevel.Warn, "*jonp*", $"# jonp: targetType={targetType.ToString ()}, targetName={targetName.ToString ()}, targetSig=`{targetSig.ToString()}`, paramCount={paramCountStr.ToString ()}, isStatic={isStaticStr.ToString ()}");
 
-			int paramCount      = 0;
-			if (!paramCountStr.IsEmpty &&
-					!int.TryParse (paramCountStr, 0, System.Globalization.CultureInfo.InvariantCulture, out paramCount)) {
-				return null;
+			int? paramCount     = null;
+			if (!paramCountStr.IsEmpty) {
+				if (!int.TryParse (paramCountStr, 0, System.Globalization.CultureInfo.InvariantCulture, out var count)) {
+					return null;
+				}
+				paramCount      = count;
 			}
+
 			bool isStatic       = false;
 			if (isStaticStr.Equals ("true", StringComparison.Ordinal)) {
 				isStatic        = true;
 			}
 
+			if (targetSig.IsEmpty && isStatic) {
+				paramCount          = paramCount ?? JniMemberSignature.GetParameterCountFromMethodSignature (jniMethodSignature);
+				paramCount++;
+				jniMethodSignature  = $"(L{jniSourceType};" + jniMethodSignature.Substring ("(".Length);
+			}
+
 			return new JniRuntime.ReplacementMethodInfo {
 					SourceJniType                   = jniSourceType,
 					SourceJniMethodName             = jniMethodName,

src/Mono.Android/Android.Runtime/AndroidRuntime.cs

@@ -182,7 +182,7 @@ internal static unsafe void Initialize (JnienvInitializeArgs* args)
 			if (args->mappingXml != IntPtr.Zero) {
 				var xml = Encoding.UTF8.GetString ((byte*) args->mappingXml, args->mappingXmlLen);
 				Logger.Log (LogLevel.Warn, "*jonp*", $"# jonp: mapping xml: len={args->mappingXmlLen}; {xml}");
-				(ReplacementTypes, ReplacementMethods) = MamXmlParser.Parse (xml);
+				(ReplacementTypes, ReplacementMethods) = MamXmlParser.ParseStrings (xml);
 			}
 #endif  // NET
 

src/Mono.Android/Android.Runtime/JNIEnv.cs

@@ -1192,7 +1192,7 @@ MonodroidRuntime::init_android_runtime (
 		native_to_managed_index = internal_timing->start_event (TimingEventKind::NativeToManagedTransition);
 	}
 
-	if (mappingXml != nullptr) {
+	if (mappingXml != nullptr && mappingXmlLen > 0) {
 		init.mappingXml             = env->GetByteArrayElements (mappingXml, nullptr);
 		init.mappingXmlLen          = mappingXmlLen;
 	}
@@ -2449,7 +2449,7 @@ JNI_OnLoad (JavaVM *vm, void *reserved)
 JNIEXPORT void JNICALL
 Java_mono_android_Runtime_init (JNIEnv *env, jclass klass, jstring lang, jobjectArray runtimeApksJava,
                                 jstring runtimeNativeLibDir, jobjectArray appDirs, jobject loader,
-                                [[maybe_unused]] jobjectArray externalStorageDirs, jobjectArray assembliesJava, jbyteArray mappingXml, jint mappingXmlLen, [[maybe_unused]] jstring packageName,
+                                [[maybe_unused]] jobjectArray externalStorageDirs, jobjectArray assembliesJava, [[maybe_unused]] jstring packageName,
                                 jint apiLevel, [[maybe_unused]] jobjectArray environmentVariables)
 {
 	monodroidRuntime.Java_mono_android_Runtime_initInternal (
@@ -2461,8 +2461,8 @@ Java_mono_android_Runtime_init (JNIEnv *env, jclass klass, jstring lang, jobject
 		appDirs,
 		loader,
 		assembliesJava,
-		mappingXml,
-		mappingXmlLen,
+		/* mappingXml */ nullptr,
+		/* mappingXmlLen */ 0,
 		apiLevel,
 		/* isEmulator */ JNI_FALSE,
 		/* haveSplitApks */ JNI_FALSE