MulticastDelegate for asynchronous callback from Java to DotNet

[Shawn Garner]

Hello,

We have a third party dll which we were trying to call from Java.

We ran into an issue with trying to do an asynchronous callback.

The C# method signature is:

public event EventHandler<ConnectionStateChangedEventArgs> ConnectionStateChanged

and ConnectionStateChangedEventArgs extends  EventArgs

When I generate the proxy to my class with the above method signature I get a Java method which has the following signature:

@net.sf.jni4net.attributes.ClrMethod("([[LSystem/EventHandler`1;)V")

    public native void addConnectionStateChanged(system.MulticastDelegate value);

I'm trying to add a MulticastDelegate and having difficulty.

I looked at an example from your a previous posting and tried to use:

new system.EventHandler(){

 Invoke(...) {do something}

}

and also 

new system.AsyncCallback() {

 Invoke(...) { do something }

}

In both cases we get this:

Exception in thread "main" System.ArgumentNullException: Value cannot be null.

Parameter name: method

   at System.Delegate.CreateDelegate(Type type, Object firstArgument, MethodInfo method, Boolean throwOnBindFailure)

   at System.Delegate.CreateDelegate(Type type, Object firstArgument, MethodInfo method)

   at net.sf.jni4net.utils.Convertor.StrongJ2CpDelegate[TRes](JNIEnv env, JniLocalHandle obj)

   ...

I saw in a previous posting that you recommended creating a C# wrapper.

We are trying to use jni4net because our companies only does development in Java.

We don't wish to have separate skill-sets, tooling, pipelines, etc for C#  so making this work without a C# wrapper would be highly preferable.

Shawn

[Shawn Garner]

Hello,

I haven't heard back from anyone so I'm re-posting.

I was just wondering if anyone had an ideas of what the issue is here and if there is some kind of work around to this issue other than creating a C# wrapper?  We are evaluating different options of integrating Java with a DotNet library and this MulticastDelegate callback issue is something that'd make us not choose jni4net.  Assuming this is an un-implemented feature we might get my company to dedicate some hours to a fix/enhancement.  We've contributed to other OSS projects in the past.

Shawn

[Pavel Šavara]

In general, you will need to understand both environments you are trying to integrate, so your comment about C# skillset  ....

I'm not sure what is wrong in your case. 

Here is event sample which should work

https://code.google.com/p/jni4net/source/browse/trunk/content/samples/winforms/java/TestForm.java

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[Shawn Garner]

We tried tried new system.EventHandler() {...} like in the TestForm.java but get the same error.

I think it may be because our EventHandler uses generics for the event args and is not just a simple plain EventHandler, 

eg:

public event EventHandler<ConnectionStateChangedEventArgs> ConnectionStateChanged

Does jni4net support event handlers with generics?

Shawn

[Pavel Šavara]

jni4net doesn't support generics