No JNI_OnLoad found skipping init > Application shutdown

Question

Folks,

I am working on an android application where I need a third party .so library. I built this third party library (with ndk-build) as per their instructions and was then looking to include this .so in to my Android project.

Therefore I followed the steps described in docs/PREBUILTS.html and successfully build the new .so in the jni/prebuilt directory. Now I tried leveraging the .so facilities by using it in a simple test android app. So what i do is :

static {
  Log.i("load so > ","load so");
  System.loadLibrary("xyz");
   }
/* The native functions */
private static native int openFile(String filename);

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    try{
        String path =  getPathForDownloadDirectoryFile();
        Log.i("file path> ", path);
        int num= openFile(path);
    }catch(Exception e){
        Log.e(">", "could not open the file");
    }
}

Now when I run my app I get a debug message saying : No JNI_OnLoad found in /data/data/com.example.myfirstapp/lib/xyz.so 0x411e6738, skipping init and then the application shuts down.

For More Info, Here is the error log :

No JNI_OnLoad found in /data/data/com.example.mysecondapp/lib/xyz.so 0x411e67a0,   skipping init
W/dalvikvm(  570): No implementation found for native    Lcom/example/mysecondapp/MainActivity;.openFile:(Ljava/lang/String;)I
D/AndroidRuntime(  570): Shutting down VM
W/dalvikvm(  570): threadid=1: thread exiting with uncaught exception (group=0x40a13300)
E/AndroidRuntime(  570): FATAL EXCEPTION: main
E/AndroidRuntime(  570): java.lang.UnsatisfiedLinkError: Native method not found:  com.example.mysecondapp.MainActivity.openFile:(Ljava/lang/String;)I
E/AndroidRuntime(  570):    at com.example.mysecondapp.MainActivity.openFile(Native  Method)
E/AndroidRuntime(  570):    at   com.example.mysecondapp.MainActivity.onCreate(MainActivity.java:31)
E/AndroidRuntime(  570):    at android.app.Activity.performCreate(Activity.java:5008)
E/AndroidRuntime(  570):    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1079)
E/AndroidRuntime(  570):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2023)
E/AndroidRuntime(  570):    at    android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2084)
E/AndroidRuntime(  570):    at android.app.ActivityThread.access$600(ActivityThread.java:130)
E/AndroidRuntime(  570):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1195)
E/AndroidRuntime(  570):    at android.os.Handler.dispatchMessage(Handler.java:99)
E/AndroidRuntime(  570):    at android.os.Looper.loop(Looper.java:137)
E/AndroidRuntime(  570):    at android.app.ActivityThread.main(ActivityThread.java:4745)
E/AndroidRuntime(  570):    at java.lang.reflect.Method.invokeNative(Native Method)
E/AndroidRuntime(  570):    at java.lang.reflect.Method.invoke(Method.java:511)
E/AndroidRuntime(  570):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786)
E/AndroidRuntime(  570):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
E/AndroidRuntime(  570):    at dalvik.system.NativeStart.main(Native Method)
W/ActivityManager(  146):   Force finishing activity com.example.mysecondapp/.MainActivity

As I could see that native implementation for the openFile() method was not found but the same xyz.so lib worked pretty neat with the original sample app from the third party. I am pretty much a starter with Android-ndk world.

Java-Android-NDK Ninjas ..any guess on what I might be missing ? I'll highly appreciate any help here :)

Answer 1

As guycole said "No JNI_OnLoad" is just a warning , your problem lies elsewhere .

As you mentioned you successfully compiled your "so" file , the problem may lie in your function signatures inside your c/C ++ code it should be something like this

JNIEXPORT jint JNICALL Java_com_your_package_class_method(JNIEnv *d, jobject e, jstring f)
{
//some action

}

The function signatures comes from the header file which is generated using javah tool.You need to generate header file and use the function signature with your package name. For different package and class names the header file and corresponding function signature will change .

worked pretty neat with the original sample app from the third party

This might be the reason its running on the sample app and not on your app.

refer: https://thenewcircle.com/s/post/49/using_ndk_to_call_c_code_from_android_apps