CODEWITHSUNDEEP
javac++swig
Driss Bounouar
Driss Bounouar

Reputation: 3242

Convert a C++ callback to Java

I have the following code in C++ (Cocos2d) :

typedef void (CCObject::*SEL_CallFunc)();
CCCallFunc * CCCallFunc::actionWithTarget(CCObject* pSelectorTarget,
    SEL_CallFunc selector) {
    CCCallFunc *pRet = new CCCallFunc();

    if (pRet && pRet->initWithTarget(pSelectorTarget)) {
        pRet->m_pCallFunc = selector;
        pRet->autorelease();
        return pRet;
    }

    CC_SAFE_DELETE(pRet);
    return NULL;
}

When converting with swig to java I get the following : 

public static CCCallFunc actionWithTarget(CCObject pSelectorTarget, SWIGTYPE_m_CCObject__f___void selector) {
    long cPtr = cocos2dxMappingJNI.CCCallFunc_actionWithTarget(CCObject.getCPtr(pSelectorTarget), pSelectorTarget,
            SWIGTYPE_m_CCObject__f___void.getCMemberPtr(selector));
    return (cPtr == 0) ? null : new CCCallFunc(cPtr, false);
}

Where SWIGTYPE_m_CCObject__f___void is just a pointer I can't use.

How do I implement this in the SWIG interface ? I've looked into this solution stackoverflow but couldn't implement it for my case.

Upvotes: 1

Views: 368

Answers (2)

John Jefferies
John Jefferies

Reputation: 1216

You probably want to look at a typemap for "SEL_CallFunc selector". The typemap squirrels the original language callback, which is called via a tramploline function. There are python examples here and here. You'll find various similar questions for java on SO.

Upvotes: 1

Samuel Audet
Samuel Audet

Reputation: 4994

I don't believe SWIG supports member function pointers in any meaningful way. However, it's possible to get it done with JavaCPP. Given this C++ code in a file named MemberFunction.h:

class MyClass {
public:
    virtual ~MyClass() { }
};

typedef void (MyClass::*MyFunction)(const char *str);

void callback(MyClass* cls, MyFunction fct, const char *str) {
    (cls->*fct)(str);
}

We can define and use the callback this way in Java:

import org.bytedeco.javacpp.*;
import org.bytedeco.javacpp.annotation.*;

@Platform(include="MemberFunction.h")
public class MemberFunction {
    static { Loader.load(); }

    public static abstract class MyClass extends Pointer {
        public MyClass() { allocate(); }
        private native void allocate();

        @Virtual public abstract void myCallback(String str);

        @Virtual @MemberGetter @Name("myCallback") 
        public static native MyFunction getMyCallback();
    }

    @Namespace("MyClass")
    public static class MyFunction extends FunctionPointer {
        public native void call(MyClass cls, String str);
    }

    public static native void callback(MyClass cls, MyFunction fct, String str);

    public static void main(String[] args) {
        MyClass cls = new MyClass() {
            public void myCallback(String str) { 
                System.out.println(str);
            }
        };
        MyFunction fct = MyClass.getMyCallback();
        callback(cls, fct, "Hello World");
    }
}

Which builds fine and outputs the expected result:

$ javac -cp javacpp.jar MemberFunction.java
$ java -jar javacpp.jar MemberFunction
$ java  -cp javacpp.jar MemberFunction
Hello World

Upvotes: 4

Related Questions