pass string parameter jni

Question

I want to pass string as a parameter in with my jni. but when I pass the string; the received string is just a meaning less characters. In fact I cant pass my desired string from java to my C# function.

what should I do?

Edit :

jin.java:

public static native void myFunc( String name);

jin.cs:

public static void java_framewindow_myFunc(int env,int object,string name)
{
messagebox.show(name);
}

and I send string "Hi" from java, but the string shown in message box is meaningless.

Edit2: here is my complete c# code :

using System;
using ObjectOrientedJNI; 
using System.Windows.Forms; 
namespace CSharpInJava { 
    public class NativeJavaMethods { 

        static void Java_FrameWindow_myFunc(int env, int obj, string name){
           messagebox.show(name);
        }
    }
}

and here is my complete java code:

import java.awt.Canvas;
import java.awt.event.ComponentEvent; 
import java.awt.event.ComponentListener;
public class FrameWindow extends Canvas { 
    int ref = 0;
      //Called by JVM to create Canvas' Peer 
    public void buttom_clicked() { 
        myFunc("hi"); 
    }
     native int myFunc(String name);
}

what am I missing?

Please provide the missing JNI code which glues these two pieces of code together. — user207421
– user207421, Commented Jun 24, 2012 at 8:36
I don't know C#, but it is good to know that Java stores string internally in UTF-16. — n0rmzzz
– n0rmzzz, Commented Jun 24, 2012 at 8:58
@houman001 tnx for your comment but I know that and in c++ and c we could use GetStringChars function but what should we do in c# to get that parameter? — Lrrr
– Lrrr, Commented Jun 24, 2012 at 9:02

n.collins · Accepted Answer · 2012-06-26 08:04:37Z

1

I have not used JNI with C#, but with C/C++ your native code should receive a jstring type, instead of string as follows:

static void Java_FrameWindow_myFunc(int env, int obj, jstring name)

Typically, JNI documentation is poor (even more so with C# it seems) so turning to the JNI Specification is a good idea. Note that JNI uses modified UTF-8 strings.

EDIT:

EJP is correct, your whole signature is incorrect. See Native Method Arguments in the JNI Spec for more detail.

static void Java_FrameWindow_myFunc( 
     JNIEnv *env,        /* interface pointer */ 
     jobject obj,        /* "this" pointer */
     jstring s)          /* argument #1 */

edited Jun 26, 2012 at 8:04

answered Jun 25, 2012 at 16:06

n.collins

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1 Comment

user207421 Over a year ago

Same applies to the 'object' parameter. It isn't an 'int': in fact it isn't even an object, it's a jclass, as the method is static. OP appears to have just made the signature up.

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