[Java.Interop] "Java Activation": API Declaration

Next can-o'-worms to start implementing: Java Activation:

http://docs.xamarin.com/guides/android/under_the_hood/architecture/#Java_Activation

There are logically two ways to create a "managed peer"/"native peer"
instance pair:

 1. By creating the managed peer, which will automagically create the
    native peer instance (see the JavaObject default constructor); or

 2. By creating the native peer.

(1) is implemented. (2) has not been, meaning at present if Java code
were to create an instance of a "native peer", no corresponding
managed peer instance would be created, and thus any `native` methods
wouldn't be registered, and things would blow up rather quickly.

How should this be exposed?

Xamarin.Android has two related methods:

  * mono.android.Runtime.register(): registers native methods for a
    Java class.
  * mono.android.TypeManager.Activate(): invoked by the Java
    constructor, and responsible for associating the native peer with
    a managed peer, creating a new managed peer if necessary.

The pattern for TypeManager.Activate() invocation is as follows:

	// Xamarin.Android constructor style
	public JavaPeerType(Args... args) {
		super (args...);
		if (getClass() == JavaPeerType.class)
			TypeManager.Activate (
					AssemblyQualifiedTypeName,
					ConstructorSignature,
					this,
					new java.lang.Object[]{ args }
			);
	}

The need for the getClass() check is so that TypeManager.Activate() is
only executed once, on the most derived native peer type, and not once
per type in the inheritance chain.

My feeling is that Runtime.register() and TypeManager.Activate()
should be more closely related, because they both operate on peer
types. (Runtime.register() is also a semantically poor name, and the
it's only in Runtime for "where else should we put it?" reasons.)

The alternative Java.Interop API? ManagedPeer.runConstructor() (and
later, ManagedPeer.registerNativeMethods()), which also alters
parameter ordering and now takes the Class for the declaring class:

	// Java.Interop constructor style:
	public JavaPeerType(Args... args) {
		super (args...);
		ManagedPeer.runConstructor (
				JavaPeerType.class,
				this,
				AssemblyQualifiedTypeName,
				ConstructorSignature,
				args...
		);
	}

This "moves" the getClass() check into ManagedPeer.runConstructor(),
allowing ManagedPeer methods to consistently take a Class instance,
and also provides possible future flexibility on behavior.

ManagedPeer.runConstructor() doesn't do anything at this time; this is
just stubbing out the API, adding the appropriate calls to our Java
"native peer" test types, and providing the initial C# implementation.

Author: jonpryor

src/Java.Interop/Java.Interop.csproj

@@ -91,10 +91,12 @@
     <Compile Include="Java.Interop\JavaProxyThrowable.cs" />
     <Compile Include="Java.Interop\JniEnvironment.Errors.cs" />
     <Compile Include="Java.Interop\JniMarshalMethod.cs" />
+    <Compile Include="Java.Interop\ManagedPeer.cs" />
   </ItemGroup>
   <ItemGroup>
     <CompileJavaInteropJar Include="java\com\xamarin\android\internal\JavaProxyObject.java" />
     <CompileJavaInteropJar Include="java\com\xamarin\android\internal\JavaProxyThrowable.java" />
+    <CompileJavaInteropJar Include="java\com\xamarin\android\ManagedPeer.java" />
   </ItemGroup>
   <Import Project="$(MSBuildExtensionsPath32)\Microsoft\Portable\$(TargetFrameworkVersion)\Microsoft.Portable.CSharp.targets" />
   <PropertyGroup>

src/Java.Interop/Java.Interop/JavaVM.cs

@@ -177,6 +177,8 @@ protected JavaVM (JavaVMOptions options)
 			}
 
 			JavaVMs.TryAdd (SafeHandle.DangerousGetHandle (), this);
+
+			ManagedPeer.Init ();
 		}
 
 		~JavaVM ()

src/Java.Interop/Java.Interop/ManagedPeer.cs

@@ -0,0 +1,50 @@
+using System;
+using System.Diagnostics;
+using System.Reflection;
+using System.Text;
+
+namespace Java.Interop {
+
+	[JniTypeInfo (ManagedPeer.JniTypeName)]
+	/* static */ class ManagedPeer : JavaObject {
+
+		internal const string JniTypeName = "com/xamarin/android/ManagedPeer";
+
+
+		static  readonly    JniPeerMembers  _members        = new JniPeerMembers (JniTypeName, typeof (ManagedPeer));
+
+		static ManagedPeer ()
+		{
+			_members.JniPeerType.RegisterNativeMethods (
+					new JniNativeMethodRegistration ("runConstructor",  RunConstructorSignature,    (Action<IntPtr, IntPtr, IntPtr, IntPtr, IntPtr, IntPtr>) RunConstructor)
+			);
+		}
+
+		ManagedPeer ()
+		{
+		}
+
+		internal static void Init ()
+		{
+			// Present so that JavaVM has _something_ to reference to
+			// prompt invocation of the static constructor & registration
+		}
+
+		public override JniPeerMembers JniPeerMembers {
+			get {return _members;}
+		}
+
+		const string RunConstructorSignature = "(Ljava/lang/Object;Ljava/lang/String;Ljava/lang/String;[Ljava/lang/Object;)V";
+
+		static void RunConstructor (
+				IntPtr jnienv,
+				IntPtr klass,
+				IntPtr n_self,
+				IntPtr n_assemblyQualifiedName,
+				IntPtr n_constructorSignature,
+				IntPtr n_constructorArguments)
+		{
+		}
+	}
+}
+

src/Java.Interop/Tests/Java.Interop-Tests.csproj

@@ -96,7 +96,7 @@
   </ItemGroup>
   <Target Name="BuildJars" Inputs="@(JavaInteropTestJar)" Outputs="@(TestJar)">
     <MakeDir Directories="$(OutputPath)it-classes" />
-    <Exec Command="javac -d &quot;$(OutputPath)it-classes&quot; @(JavaInteropTestJar -&gt; '%(Identity)', ' ')" />
+    <Exec Command="javac -d &quot;$(OutputPath)it-classes&quot; -classpath &quot;$(OutputPath)\java-interop.jar&quot; @(JavaInteropTestJar -&gt; '%(Identity)', ' ')" />
     <Exec Command="jar cf &quot;$(OutputPath)interop-test.jar&quot; -C &quot;$(OutputPath)it-classes&quot; ." />
   </Target>
   <ItemGroup>

src/Java.Interop/Tests/java/com/xamarin/interop/CallNonvirtualBase.java

@@ -2,6 +2,15 @@
 
 public class CallNonvirtualBase {
 
+	public CallNonvirtualBase () {
+		com.xamarin.android.ManagedPeer.runConstructor (
+				CallNonvirtualBase.class,
+				this,
+				"Java.InteropTests.CallNonvirtualBase, Java.Interop-Tests, Version=0.0.0.0, Culture=neutral, PublicKeyToken=null",
+				""
+		);
+	}
+
 	boolean methodInvoked;
 	public void method () {
 		System.out.println ("CallNonvirtualBase.method() invoked!");

src/Java.Interop/Tests/java/com/xamarin/interop/CallNonvirtualDerived.java

@@ -2,6 +2,15 @@
 
 public class CallNonvirtualDerived extends CallNonvirtualBase {
 
+	public CallNonvirtualDerived () {
+		com.xamarin.android.ManagedPeer.runConstructor (
+				CallNonvirtualDerived.class,
+				this,
+				"Java.InteropTests.CallNonvirtualDerived, Java.Interop-Tests, Version=0.0.0.0, Culture=neutral, PublicKeyToken=null",
+				""
+		);
+	}
+
 	boolean methodInvoked;
 	public void method () {
 		System.out.println ("CallNonvirtualDerived.method() invoked!");

src/Java.Interop/Tests/java/com/xamarin/interop/CallNonvirtualDerived2.java

@@ -1,4 +1,13 @@
 package com.xamarin.interop;
 
 public class CallNonvirtualDerived2 extends CallNonvirtualDerived {
+
+	public CallNonvirtualDerived2 () {
+		com.xamarin.android.ManagedPeer.runConstructor (
+				CallNonvirtualDerived2.class,
+				this,
+				"Java.InteropTests.CallNonvirtualDerived2, Java.Interop-Tests, Version=0.0.0.0, Culture=neutral, PublicKeyToken=null",
+				""
+		);
+	}
 }

src/Java.Interop/Tests/java/com/xamarin/interop/CallVirtualFromConstructorBase.java

@@ -3,6 +3,13 @@
 public class CallVirtualFromConstructorBase {
 
 	public CallVirtualFromConstructorBase (int value) {
+		com.xamarin.android.ManagedPeer.runConstructor (
+				CallVirtualFromConstructorBase.class,
+				this,
+				"Java.InteropTests.CallVirtualFromConstructorBase, Java.Interop-Tests, Version=0.0.0.0, Culture=neutral, PublicKeyToken=null",
+				"System.Int32",
+				value
+		);
 		calledFromConstructor (value);
 	}
 

src/Java.Interop/Tests/java/com/xamarin/interop/CallVirtualFromConstructorDerived.java

@@ -4,6 +4,13 @@ public class CallVirtualFromConstructorDerived extends CallVirtualFromConstructo
 
 	public CallVirtualFromConstructorDerived (int value) {
 		super (value);
+		com.xamarin.android.ManagedPeer.runConstructor (
+				CallVirtualFromConstructorDerived.class,
+				this,
+				"Java.InteropTests.CallVirtualFromConstructorDerived, Java.Interop-Tests, Version=0.0.0.0, Culture=neutral, PublicKeyToken=null",
+				"System.Int32",
+				value
+		);
 	}
 
 	public native void calledFromConstructor (int value);

src/Java.Interop/Tests/java/com/xamarin/interop/TestType.java

@@ -2,6 +2,15 @@
 
 public class TestType {
 
+	public TestType () {
+		com.xamarin.android.ManagedPeer.runConstructor (
+				TestType.class,
+				this,
+				"Java.InteropTests.TestType, Java.Interop-Tests, Version=0.0.0.0, Culture=neutral, PublicKeyToken=null",
+				""
+		);
+	}
+
 	public  void    runTests () {
 		int n = getInt32Value ();
 		if (getInt32Value() != 42)