requestaudiofocus 的正确参数是什么？

Question

我是 Android 和 Java 的新手。我一直在使用 Android 开发人员和其他网站提供的 MediaPlayer 和 AudioManager 示例。

我注意到，对于 requestAudioFocus() 的调用似乎使用了两个单独的签名。例如，来自 http://developer.android.com/guide/topics/media/mediaplayer.html 网站有：

AudioManager audioManager = (AudioManager) getSystemService(Context.AUDIO_SERVICE);
int result = audioManager.requestAudioFocus(this, AudioManager.STREAM_MUSIC,
    AudioManager.AUDIOFOCUS_GAIN);

if (result != AudioManager.AUDIOFOCUS_REQUEST_GRANTED) {
    // could not get audio focus.
}

加上以下文字：

"The first parameter to requestAudioFocus() is an AudioManager.OnAudioFocusChangeListener, whose onAudioFocusChange() method is called whenever there is a change in audio focus. Therefore, you should also implement this interface on your service and activities. For example:" （使用以下代码：）

class MyService extends Service
                implements AudioManager.OnAudioFocusChangeListener {
    // ....
    public void onAudioFocusChange(int focusChange) {
        // Do something based on focus change...
    }
}

然后从站点： http://developer.android.com/training/managing-audio/audio-focus.html 有：

OnAudioFocusChangeListener afChangeListener = new OnAudioFocusChangeListener() {
    public void onAudioFocusChange(int focusChange) {
        if (focusChange == AUDIOFOCUS_LOSS_TRANSIENT) {
            // Pause playback
        } else if (focusChange == AudioManager.AUDIOFOCUS_GAIN) {
            // Resume playback 
        } else if (focusChange == AudioManager.AUDIOFOCUS_LOSS) {
            am.unregisterMediaButtonEventReceiver(RemoteControlReceiver);
            am.abandonAudioFocus(afChangeListener);
            // Stop playback
        }
    }
};

AudioManager am = mContext.getSystemService(Context.AUDIO_SERVICE);
...

// Request audio focus for playback
int result = am.requestAudioFocus(afChangeListener,
                                 // Use the music stream.
                                 AudioManager.STREAM_MUSIC,
                                 // Request permanent focus.
                                 AudioManager.AUDIOFOCUS_GAIN);

if (result == AudioManager.AUDIOFOCUS_REQUEST_GRANTED) {
    am.registerMediaButtonEventReceiver(RemoteControlReceiver);
    // Start playback.
}

我在许多网站上看到过这种二分法，它们提供了处理音频焦点变化的示例代码。我的理解是 "this" 提供应用程序当前状态的上下文。我不明白为什么在某些情况下 "this" 是正确的参数，而在其他情况下，更改侦听器的句柄在调用 requestAudioFocus() 时是正确的参数。

事实上，我提供的第一个示例指出第一个参数应该是 AudioManager.OnAudioFocusChangeListener。但是使用了"this"。

如果您能解释为什么使用 "this" 而不是 AudioManager.OnAudioFocusChangeListener 作为参数，我们将不胜感激。

Answer 1

它总是需要一个 onAudioFocusedChangeListener。在传递这个的情况下，当前class实现了onAudioFocusChangeListener接口。

requestaudiofocus 的正确参数是什么？

What are the correct arguments for requestaudiofocus?

java

audio

android