Android NDK: calling java method from JNI C class

问题:

I have JNI method where I am trying to call Java method. Here is my JNI code

void DummySink::afterGettingFrame(unsigned frameSize, unsigned numTruncatedBytes,
                  struct timeval presentationTime, unsigned /*durationInMicroseconds*/) {

     __android_log_print(ANDROID_LOG_VERBOSE, "RTSP", "Frame: %c", propRec->sPropBytes);
     jmethodID mid;
     jclass handlerClass = env9->FindClass("ob/android/Stream");
     if (handlerClass == NULL) {
         __android_log_print(ANDROID_LOG_VERBOSE, "RTSP-Error", "Class");
     }
     mid = env9->GetMethodID(handlerClass, "onResponse", "([B)V");
     if (mid == NULL) {
         __android_log_print(ANDROID_LOG_VERBOSE, "RTSP-Error", "Method");
     }

     jbyteArray jbArray = env9->NewByteArray((int)propRec->sPropLength);
     env9->SetByteArrayRegion(jbArray, 0, (int)propRec->sPropLength, (jbyte*)propRec->sPropBytes);

     //jobject theClass = env9->FindClass("ob/android/Stream");

     env9->CallVoidMethod(handlerClass, mid, jbArray);

}

Here is the Java code that I have

public void onResponse(byte[] str) 
    { 
        Log.v("Response", "Java");
    }

I am receiving following crash

03-08 16:01:05.915: W/dalvikvm(17552): JNI WARNING: can't call Lob/android/Stream;.onResponse on instance of Ljava/lang/Class;
03-08 16:01:05.915: W/dalvikvm(17552):              in Lob/android/Stream;.stream:()V (CallVoidMethodV)

After applying Mah's answer, here is the exception I am receiving

03-08 16:40:20.646: W/dalvikvm(4076): JNI WARNING: JNI method called with exception pending
03-08 16:40:20.646: W/dalvikvm(4076):              in Lob/android/Stream;.stream:()V (NewByteArray)
03-08 16:40:20.646: W/dalvikvm(4076): Pending exception is:
03-08 16:40:20.646: I/dalvikvm(4076): java.lang.NoSuchMethodError: no method with name='onResponse' signature='([B)V' in class Lob/android/Stream;
03-08 16:40:20.646: I/dalvikvm(4076):   at ob.android.Stream.stream(Native Method)
03-08 16:40:20.646: I/dalvikvm(4076):   at ob.android.Stream.<init>(Stream.java:28)
03-08 16:40:20.654: I/dalvikvm(4076):   at ob.android.MainActivity.startRecording(MainActivity.java:203)

Now onResponse method is static.

回答1:

Your Java method is an instance method (not static), but your native code isn't referring to any specific instance of ob.android.Stream to call onResponse() for.

When calling CallVoidMethod(), the first parameter is to be the instance (object) you're running the method against, not the class itself. The class itself would be used if you were using CallStaticVoidMethod().

回答2:

I would like to add one more solution to the NoSuchMethodError problem, that although might not be the case here, might save some of you a lot of hours of debugging.

For me, there was a proguard config file that I had to edit. Otherwise all non-static java methods that aren't called in the java code, get optimized out and the native C++ code isn't able to find them.