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1 Reply Latest reply: Apr 13, 2012 2:41 AM by EJP RSS

Re: Android JNI Call

930422 Newbie
Currently Being Moderated
(Thread-hijack post, split off to be its own inquiry)


----

hi,
I have tried writing a jni call for the simple c code. when i try to install this on the phone running 2.3.3 it doesnt install, sometimes even if it installs then it is being force closed.Please help me with this. the code details are as follows:

The java code of which i generate the header file.

package com.hosa;

public class edgejava{
     static{
          System.loadLibrary("edgejava");
     }
     public native int main();
}

the generated header file is as below

/* DO NOT EDIT THIS FILE - it is machine generated */
#include <jni.h>
/* Header for class com_hosa_edgejava */

#ifndef Includedcom_hosa_edgejava
#define Includedcom_hosa_edgejava
#ifdef __cplusplus
extern "C" {
#endif
/*
* Class: com_hosa_edgejava
* Method: main
* Signature: ()I
*/
JNIEXPORT jint JNICALL Java_com_hosa_edgejava_main
(JNIEnv *, jobject);

#ifdef __cplusplus
}
#endif
#endif


the implementation of native function is as below

#include "com_hosa_edgejava.h"
#include <jni.h>
#include <cv.h>
#include <highgui.h>

using namespace cv;

JNIEXPORT jint JNICALL Java_com_pes_edgejava_main(JNIEnv *, jobject){
VideoCapture cap(0); // open the default camera
if(!cap.isOpened()) // check if we succeeded
return -1;

Mat edges;
namedWindow("edges",CV_WINDOW_AUTOSIZE);
for(;;)
{
Mat frame;
cap >> frame; // get a new frame from camera
cvtColor(frame, edges, CV_BGR2GRAY);
GaussianBlur(edges, edges, Size(7,7), 1.5, 1.5);
Canny(edges, edges, 0, 30, 3);
imshow("edges", edges);
if(waitKey(30) >= 0) break;
}
// the camera will be deinitialized automatically in VideoCapture destructor
return 0;
}

the android.mk file

LOCAL_PATH := $(call my-dir)

include $(CLEAR_VARS)

include /home/srijith/android-opencv/OpenCV-2.3.1/share/OpenCV/OpenCV.mk

LOCAL_MODULE := edgejava
LOCAL_SRC_FILES := edgecpp.cpp
LOCAL_LDLIBS += -llog -ldl


include $(BUILD_SHARED_LIBRARY)


the application.mk


APP_MODULES := edgejava
APP_STL := gnustl_static
APP_CPPFLAGS := -frtti -fexceptions


the activity file is as follows

package com.hosa;

import android.app.Activity;
import android.os.Bundle;

public class Andedge2Activity extends Activity {
     edgejava nativelib;
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);

nativelib= new edgejava();
int i=nativelib.main();
System.out.println("value returned to andedgeactivity "+i);
}
}

All necessary changes to the manifest has been done like mention of use of camera and permissions has been set.
  • 1. Re: Android JNI Call
    EJP Guru
    Currently Being Moderated
    The java code of which i generate the header file.

    package com.hosa;

    public class edgejava{
         static{
              System.loadLibrary("edgejava");
         }
         public native int main();
    }
    So the class is com.hosa.edgejava.
    the generated header file is as below

    /* DO NOT EDIT THIS FILE - it is machine generated */
    #include <jni.h>
    /* Header for class com_hosa_edgejava */

    #ifndef Includedcom_hosa_edgejava
    #define Includedcom_hosa_edgejava
    #ifdef __cplusplus
    extern "C" {
    #endif
    /*
    * Class: com_hosa_edgejava
    * Method: main
    * Signature: ()I
    */
    JNIEXPORT jint JNICALL Java_com_hosa_edgejava_main
    So the header has been generated from the current .java file.
    the implementation of native function is as below
    ...
    JNIEXPORT jint JNICALL Java_com_pes_edgejava_main(JNIEnv *, jobject){
    So you have either got the package name wrong, or changed it since you generated this file with javah.

    So fix that.