APP request/abandon Audiofocus的接口

1、App 申请音频焦点代码，举例：

    private void requestAudioFocus(int focusType) {
        int result;
        if (android.os.Build.VERSION.SDK_INT >= 26) {
            AudioFocusRequest focusRequest;
            focusRequest = new AudioFocusRequest.Builder(focusType)
                    .setAudioAttributes((AudioAttributes) mAudioAttributes.unwrap())
                    .setOnAudioFocusChangeListener(mAudioFocusListener)
                    .build();
            result = mAudioManager.requestAudioFocus(focusRequest);
        } else {
            result = mAudioManager.requestAudioFocus(mAudioFocusListener,
                    AudioManager.STREAM_MUSIC,
                    focusType);
        }
        if (result == AudioManager.AUDIOFOCUS_REQUEST_FAILED) {
            mAudioFocused = false;
        } else if (result == AudioManager.AUDIOFOCUS_REQUEST_GRANTED) {
            mAudioFocused = true;
        } else if (result == AudioManager.AUDIOFOCUS_REQUEST_DELAYED) {
            mAudioFocused = false;
        }
    }

如果申请失败了，就用AudioManager.AUDIOFOCUS_REQUEST_FAILED。

下面的例子是错的：LOSS是丢失焦点。

我们来看一下mAudioFocusListener是怎么实现的？