Question

I want to use OpenCV 2.4.0 native code in Android 2.3.3. For that, I used NDK release-8 to build lib.so shared libraries using the ndk-build.cmd script on Windows 7. I used Eclipse to create a project and build the .apk file.

Here’s the problem, I get an UnsatisfiedLinkError exception thrown when I try to load the shared libraries using System.loadLibrary() in the Java code. I have tried doing the same thing with the hello-jni sample in NDK, and it works absolutely fine.

I followed instructions on this page for creating a project and for writing the Android.mk and Application.mk files.

Here’s my java code:

package my.package.ocvtest1
// import android.foo.bar statements

public class OCVTest1 extends Activity
{

    public void onCreate(Bundle savedInstance)
    {
        super.onCreate(Bundle savedInstance)
        // code to display strings returned by native functions
    }

    public native String funtionName1();
    public native String functionName2();

    static
    {
        System.loadLibrary("ocvtest1");
    }

}

Here’s the (Project dir)/jni/ocvtest1.c file which implement native functions:

#include <jni.h>

// Other header files and some global variables

jstring Java_my_package_ocvtest1_OCVTest1 (JNIEnv *ptr, jobject obj)
{
    // code here
}

jstring Java_my_package_ocvtest1_OCVTest1_functionName2 (JNIEnv *ptr, jobject obj)
{
    // code here   
}

// End of file

I’ve googled this problem and tried the solutions, and even after implementing those solutions I get this exception. Here’s all the things I’ve tried till now:

Used dynamic linking by copying the libopencv_java.so and the static *.a library files into the (Project dir)/libs and (Project dir)/obj/local folders and changed static block of java source code to

static
{
    System.loadLibrary("opencv_java");
    System.loadLibrary("ocvtest");
}

Used static linking by adding OPENCV_LIB_TYPE:=STATIC as below

include $(CLEAR_VARS)
OPENCV_LIB_TYPE:=STATIC
include (<Path to Opencv.mk>)

Included header file generated by executing javah.exe my.package.OCVTest1 in the command prompt while using dynamic linking.

Changed armeabi-v7a to armeabi for the abi version variable in Application.mk file.

For all the above changes, to make sure that the library files were loaded into the app’s lib folder, I executed

adb push <path to library on disk> <path to /lib in app> 

which copied the library files into the proper directory on the phone.

After trying all of this fixes, I’m still not able to resolve this exception.

Answer 1

Used dynamic linking by copying the libopencv_java.so and the static
*.a library files into the (Project dir)/libs and (Project dir)/obj/local folders and changed static block of java source code to

You have to copy only libopencv_java.so (*.a file is not needed) to (Project dir)/libs/armeabi-v7a.

Also you have:

public native String funtionName1();

But in native c code there are only these functions:

jstring Java_my_package_ocvtest1_OCVTest1 (JNIEnv *ptr, jobject obj) // mistake?
jstring Java_my_package_ocvtest1_OCVTest1_functionName2 (JNIEnv *ptr, jobject obj)

It seems that name of the first function is wrong.

That should fix your problem.