jni开发-GetMethodID与CallObjectMethod的坑

在java层中声明一个方法用于创建一个audiotrack，在C层中调用这个方法并获取audiotrack对象。

先看下面的代码：SuPlayer.java

public AudioTrack createAudioTrack(int sampleRateInHz, int nb_channels) {
//固定格式的音频码流
int audioFormat = AudioFormat.ENCODING_PCM_16BIT;
//声道布局
int channelConfig;
if (nb_channels == 1) {
channelConfig = android.media.AudioFormat.CHANNEL_OUT_MONO;
} else if (nb_channels == 2) {
channelConfig = android.media.AudioFormat.CHANNEL_OUT_STEREO;
} else {
channelConfig = android.media.AudioFormat.CHANNEL_OUT_STEREO;
}

int bufferSizeInBytes = AudioTrack.getMinBufferSize(sampleRateInHz, channelConfig, audioFormat);

AudioTrack audioTrack = new AudioTrack(
AudioManager.STREAM_MUSIC,
sampleRateInHz, channelConfig,
audioFormat,
bufferSizeInBytes, AudioTrack.MODE_STREAM);
//播放
//audioTrack.play();
//写入PCM
//audioTrack.write(audioData, offsetInBytes, sizeInBytes);
return audioTrack;
}

//只播放视频
public static native int playVideo(String url, Surface surface);

//音视频同步播放
public native void playSyncVideo(String url, Surface surface);

C层实现：

JNIEXPORT void
JNICALL Java_com_eebbk_suplayer_SuPlayer_playSyncVideo(JNIEnv *env, jobject thiz, jstring inputPath_, jobject surface) {
int i = 1;
//JNI begin------------------
jclass player_class = env->GetObjectClass(jthiz);//获取当前类的class
//获取methodID，调java层的createAudioTrack函数，返回值是(II)Landroid/media/AudioTrack;
//详细参考：http://hubeihuyanwei.blog.163.com/blog/static/28205284201282911925396/
jmethodID create_audio_track_mid = env->GetMethodID(player_class, "createAudioTrack",
"(II)Landroid/media/AudioTrack;");
if (create_audio_track_mid == NULL) {
LOGE("%s", "createAudioTrack 方法没找到！\n");
}
//获取audio_track对象，传入methodid、java层中对应方法的形参
jobject audio_track = env->CallObjectMethod(jthiz, create_audio_track_mid, i, i);
//调用AudioTrack.play方法
jclass audio_track_class = env->GetObjectClass(audio_track);
jmethodID audio_track_play_mid = env->GetMethodID(audio_track_class, "play", "()V");
env->CallVoidMethod(audio_track, audio_track_play_mid);
//AudioTrack.write
jmethodID audio_track_write_mid = env->GetMethodID(audio_track_class, "write",  "([BII)I");
LOGE("%s", "44444");
//JNI end------------------
}

就这么简单的调用顺序，为什么要写这篇笔记呢？？？因为在写这个的时候，把SuPlayer.java中public AudioTrack createAudioTrack(int sampleRateInHz, int nb_channels)这个方法写成了静态方法public static AudioTrack createAudioTrack(int sampleRateInHz, int nb_channels)。导致排查的时候一直以为env->GetMethodID（）这个函数写的有问题。