Calling C# method within a Java program

Question

C# methods cannot be called directly in Java using JNI due to different reasons. So first we have to write a wrapper for C# using C++ then create the dll and use it through JNI in Java.

I have problem in calling C# code in C++. I'm adding C# .netmodule file to a C++ project. Code is pasted below. Please guide me if i'm doing anything wrong.

This is my managed C++ class UsbSerialNum.h:

#using <mscorlib.dll>
#include <iostream>
#using "UsbSerialNumberCSharp.netmodule"

using namespace std;

using namespace System;

public __gc class UsbSerialNum
{
    public:

        UsbSerialNumberCSharp::UsbSerialNumberCSharp __gc *t;

        UsbSerialNum() {
            cout<<"Hello from C++";
            t = new UsbSerialNumberCSharp::UsbSerialNumberCSharp();
        }

        void CallUsbSerialNumberCSharpHello() {
            t->hello();
        }
};

C# UsbSerialNumberCSharp.cs file from which i've created the .netmodule file:

using System.Collections.Generic;
using System.Text;

namespace UsbSerialNumberCSharp
{
    public class UsbSerialNumberCSharp
    {

        public UsbSerialNumberCSharp(){
            Console.WriteLine("hello");
        }

        public static void hello()
        {
            Console.WriteLine("hello");
        }

        public void helloCSharp ()
        {
            Console.WriteLine("helloCSharp");
        }
    }
}

Here is my main makeDLL.cpp file from which makeDLL.dll is created:

#include "jni.h"
#include <iostream>


// This is the java header created using the javah -jni command.
#include "testDLL.h"


// This is the Managed C++ header that contains the call to the C#
#include "UsbSerialNum.h"

using namespace std;


JNIEXPORT void JNICALL Java_testDLL_hello
(JNIEnv *, jobject) {

    // Instantiate the MC++ class.
    UsbSerialNum* serial = new UsbSerialNum();
    serial->CallUsbSerialNumberCSharpHello();
}

Here is my java class:

public class testDLL {

    static {
        System.loadLibrary("makeDLL");
    }

    /**
     * @param args
     */
    public static void main (String[] args) {
        //        new testDLL().GetUSBDevices("SCR3", 100);
        new testDLL().hello();
    }

    public native void hello();

}

EDIT:

If i simply ignore the call to UsbSerial.h in my main file i.e. use simple C++ then my code is working fine in Java. Basically C++ managed class is not working properly. Please guide me. Thanks.

What's the problem? Is this managed C++? I don't recognize the __gc bits — flipchart
– flipchart, Commented Nov 18, 2011 at 11:05
@BumbleBee: when pointer of UsbSerial serial* is created and constructor is called. That is where i'm getting the error. — HashimR
– HashimR, Commented Nov 18, 2011 at 11:28
@flipchart: __gc is used to make a garbage collectable instance to be compatible with java... — HashimR
– HashimR, Commented Nov 18, 2011 at 11:29

Viruzzo · Accepted Answer · 2011-11-18 15:08:59Z

8

It would be useful to know what you need this interoperability for exactly. In any case, you should look into IKVM; alternatively you can (as has been suggested for a similar problem) use COM as a bridge: expose the C#/CLR as a COM interface and then use com4j in Java.

answered Nov 18, 2011 at 15:08

Viruzzo

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1 Comment

HashimR Over a year ago

I want to get the serial number of all attached USBs, have already written the code in C#, want to use it in Java.

Umer Hayat · Accepted Answer · 2011-11-28 05:34:25Z

0

+50

You can avoid C# and still can query WMI using C++ only. See Using WMI to call method on objects

answered Nov 28, 2011 at 5:34

Umer Hayat

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