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JNI call restarts the calling JAVA Activity

asked 2013-03-08 08:40:15 -0600

sumitsh87 gravatar image

updated 2013-03-08 08:45:52 -0600

I am stuck at a strange problem, pretty strange!!

Problem : In the following project, a native method is called from java android using JNI call. Whenever the native method returns, the android activity restarts (oncreate callback method is called again). I confirmed this using a Log inside the "oncreate()". It all results into a recursion!! why??

Please help :(

JAVA CODE

   public class Brahma extends Activity {

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.brahma);
    Log.v("Sumit","on create called");
    TextView text=(TextView)findViewById(R.id.textView);
    ImageView img=(ImageView)findViewById(R.id.imageView);
    Mat inputFrame= new Mat();
    String str =JNIMessage(inputFrame.getNativeObjAddr());
    text.setText(str);

    Bitmap bmp = Bitmap.createBitmap(inputFrame.cols(), inputFrame.rows(),    
                                             Bitmap.Config.ARGB_8888);
        Utils.matToBitmap(inputFrame, bmp);
    img.setImageBitmap(bmp);


}


public static native String JNIMessage(long l);

static 
{
    if (!OpenCVLoader.initDebug()) 
    {
        // Handle initialization error
    } else
        System.loadLibrary("brahma");
}

}

NATIVE CODE

  using namespace std;
  using namespace cv;

  extern "C"
  {
 JNIEXPORT jstring JNICALL Java_com_example_brahma_Brahma_JNIMessage(JNIEnv* , jobject, jlong);

 JNIEXPORT jstring JNICALL Java_com_example_brahma_Brahma_JNIMessage(JNIEnv* env, jobject      
  thiz,jlong addr)
  {
   static int i=0;
   char buffer[100];
   sprintf(buffer, "native function called : time : %d", i++);
       __android_log_print(ANDROID_LOG_INFO, "Sumit", buffer);
   Mat& frame  = *(Mat*)addr;
       VideoCapture cap(0); // open the default camera
   cap>>frame;
   return env->NewStringUTF("Success");

  }

   }
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answered 2013-03-08 13:55:35 -0600

rics gravatar image

Are you sure that you can open the default camera? You simply return Success without a check.

First I would eliminate the videocapture handling from the native code and see if the native call works from the onCreate.

Anyway have you set the following in Android.mk?

OPENCV_CAMERA_MODULES:=on
OPENCV_INSTALL_MODULES:=on

Have you set camera rights in AndroidManifest.xml?

<uses-permission android:name="android.permission.CAMERA"/>

Do you specifically need static initialization? If so then you need to configure your environment according to this description. Otherwise it is recommended to use async initialization.

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Asked: 2013-03-08 08:40:15 -0600

Seen: 614 times

Last updated: Mar 08 '13