Java – JNI CALL changes jclass parameters or how to get jobject from jclass parameters

I’m testing some features using Android, JNI, and NDK.

I HAVE THE FOLLOWING JAVA CLASS:

import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.widget.TextView;

public class JNITest extends Activity {
    private int contador;
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);

contador = 0;
        TextView label = (TextView)findViewById(R.id.Text);
        label.setText(Integer.toString(contador));
    }

public void addClick(View addButton) {
        nativeAdd(1);
        TextView label = (TextView)findViewById(R.id.Text);
        label.setText(Integer.toString(contador));
    }

private static native void nativeAdd(int value);

static {
        System.loadLibrary("JNITest01");
    }
}

I’ve generated the header file with javah -jni:

#include <jni.h>
/* Header for class es_xxxxx_pruebas_JNITest */

#ifndef _JNITestNative
#define _JNITestNative
#ifdef __cplusplus
extern "C" {
#endif
/*
 * Class:     com_xxxxx_tests_JNITest
 * Method:    nativeAdd
 * Signature: (I)V
 */
JNIEXPORT void JNICALL Java_com_xxxxx_tests_JNITest_nativeAdd
(JNIEnv *, jclass, jint);

#ifdef __cplusplus
}
#endif
#endif

As you can see, the second parameter is the jclass type.

I would like to know how to change jclass for jobject parameter.

I need a jobject parameter to get the value from the field of the class that calls this native function.

How do I change the method signature? Or how to get jobject from jclass parameter?

Thank you.

Static methods do not have access to the object (implicitly this parameter), only other static methods/properties of the class. That’s why your native method has jclass instead of jobject.

So, change your Java method to a non-static method and regenerate your header file.

By the way, you

can create Java objects from JNI, but in this case I think you want to be able to change the value of the member variable contador so that doesn’t help you.