IKVM C# to Java Interop with Callback using IKVM

Question

I've started using IKVM to translate Java libs into .NET CIL. I can successfully write a C# program that pulls in (inproc) a translated Java assembly as a reference and make calls to the translated Java code.

My question is, is anyone familiar w/ how to make calls (callbacks) from Java to C# using IKVM? I've been looking for a good tutorial or explanation but haven't seen one yet.

Any help is appreciated. Thanks,

mj

Answer 1

Ladies and Gentlemen, I figured out my own question. Code first followed by steps.

Java Class

public class TestClass {
private cli.CSharpLibrary.Library m_lib = null;

public void AddDelegate( cli.CSharpLibrary.Library lib )
{
    m_lib = lib;
}

public void FireDelegate()
{
    if( m_lib != null )
    {
        m_lib.ExecuteRunnableDelegate();
    }
}

public void PrintInt()
{
    System.out.print(23);
}
}

C# Class

using ikvm.runtime;
using CSharpLibrary;

namespace CSharp
{
  class Program
  {
public static void DelegateTarget()
{
  Console.WriteLine("DelegateTarget Executed!");
}

static void Main(string[] args)
{
  Library lib = new Library();
  lib.m_runnableDelegate = new Delegates.RunnableDelegate(DelegateTarget);

  TestClass tc = new TestClass();
  tc.AddDelegate(lib);
  tc.FireDelegate();

}
}
}

1) Write your Java app

2) Convert your *.class files into a jar file (jar -cf myjar.jar *.class)

3) Convert the jar file into a .NET assembly (ikvmc -reference:csharpassembly.dll myjar.jar)

Should work at this point. You can run your C# program, have it call the converted Java program and vice versa. Watch out for the "-reference" flag on the ikvmc call. This tells IKVM when it's converting the Java code that csharpassembly.dll has some class definitions that it needs to watch out for.

Answer 2

JaapM, I think CSharpLibrary in mj_'s solution is a transient class from third C# DLL project (cshardassembly.dll), that he compiles first and then shares between actual java and C# code. It doesn't matter what's in it, the idea is that both sides have a piece of code (class) known in advance. This is overkill, if I'm correct.

I know, it's a long time passed but I would like to post a short solution here that works for me, cuz I wasted too much time on it and IKVM documentation is very poor:

Java:

package what.ever.package;
import cli.System.Delegate;
import cli.System.Int32;
public class SomeJavaClass
{
    public static void setCallback(Delegate callback)
    {
        // I call delegate in static setter to keep example short, 
        // but you may save it and call later...
        Int32 result = (Int32)callback.DynamicInvoke("hello", "world");
        System.out.println("Callback returned [" + result + "]");
    }
}

Don't forget to convert mscorlib.dll into jar and attach it to your java project to support cli imports. build it and run ikvmc.exe on jar with -target:library parameter and add resulting DLL into C# project.

C#:

using what.ever.package
class Program
{
    // signature of delegate must match target function.
    public delegate Int32 TheDelegateItself(String a, String b);

    // callback that we pass into java.
    public static Int32 DelegateTarget(String a, String b)
    {
        Console.WriteLine("DelegateTarget Executed: [" + a + ", " + b + "]!");
        return 42;
    }

    static void Main(string[] args)
    {
        // again, static call to keep it short
        // but you may want a class instance in most cases.
        SomeJavaClass.setCallback(new TheDelegateItself(DelegateTarget));
    }
}

output:

DelegateTarget Executed: [hello, world]!
Callback returned [42]