JNI 函数调用上的 ClassCastException：CallVoidMethod

Question

我正在尝试从 Android 应用程序中的本机 C++ 代码调用 java 方法。当我尝试调用我的 Java 方法时发生异常。我看过几个例子，但我无法弄清楚我做错了什么。请帮助我。

Java 边:

public class UsbAudioRecorder {

private UsbAudioRecordListener listener;

UsbAudioRecorder(UsbAudioRecordListener listener){
    this.listener = listener;
}    

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

public native int native_setupConnection(final int fd, final String usbfs_path);

public native void start();

public void received(byte[] audio){
    listener.recorded(audio);
}
//some more methods...
}

本机代码：

static jclass class_usbAudioRecorder = NULL;
static jmethodID methId_UsbAudioRecorder_received;

JNIEXPORT jint JNICALL Java_com_example_soundcard_UsbAudioRecorder_native_1setupConnection
(JNIEnv *env , jobject obj, jint fd, jstring usbfs_path){

// Get the objects class
jclass clazz = env->GetObjectClass(obj);
if (!clazz) {
    LOGD("Could not find class");
    error = LIBUSB_ERROR_OTHER;
}
class_usbAudioRecorder =  (jclass) env->NewGlobalRef(clazz);

env->DeleteLocalRef(clazz);

 // Get the callbacks method id
methId_UsbAudioRecorder_received = env->GetMethodID(class_usbAudioRecorder,"received", "([B)V");
if (!methId_UsbAudioRecorder_received) {
    LOGD("Could not find method");
    env->DeleteGlobalRef((jobject) class_usbAudioRecorder);
    error = LIBUSB_ERROR_OTHER;
    goto err;
}

// event handle callback
static void cb_trans(struct libusb_transfer* transfer){
     // Create a jbyteArray.
    jbyteArray  audioArray = env->NewByteArray(PACKET_SIZE * transfer->num_iso_packets);

//here i populate jbyteArray with data

// Callback
env->CallVoidMethod(class_usbAudioRecorder, methId_UsbAudioRecorder_received, audioArray);

// cleaning up
env->DeleteLocalRef(audioArray);
jthrowable exc;
exc = env->ExceptionOccurred();
if (exc) {
    env->ExceptionDescribe();

}
if (env->ExceptionCheck()) {
    LOGD("Exception while trying to pass sound data to java");
    env->ExceptionClear();
    return;
}

异常输出：

10-27 15:19:55.658 11890-12476/com.example.soundcard W/System.err: java.lang.ClassCastException: [B cannot be cast to com.example.soundcard.UsbAudioRecorder 10-27 15:19:55.658 11890-12476/com.example.soundcard W/System.err: at java.lang.Class.cast(Class.java:1278) 10-27 15:19:55.663 11890-12476/com.example.soundcard W/System.err: at com.example.soundcard.UsbAudioRecorder.start(Native Method) 10-27 15:19:55.663 11890-12476/com.example.soundcard W/System.err: at com.example.soundcard.MainActivity$OnClickListener.run(MainActivity.java:279) 10-27 15:19:55.663 11890-12476/com.example.soundcard W/System.err:
at java.lang.Thread.run(Thread.java:841)

Answer 1

我找到了解决办法。只是为了节省别人一些时间：调用非静态方法时，您需要将 class 实例作为 jobject 传递给 CallVoidMethod。我的错误是使用仅适用于静态方法的 jclass 来调用它。

JNI 函数调用上的 ClassCastException：CallVoidMethod

ClassCastException on JNI function call: CallVoidMethod

c++

java

java-native-interface

android