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请求焦点：

/**
     *  Request audio focus.
     *  Send a request to obtain the audio focus
     *  @param l the listener to be notified of audio focus changes
     *  @param streamType the main audio stream type affected by the focus request
     *  @param durationHint use {@link #AUDIOFOCUS_GAIN_TRANSIENT} to indicate this focus request
     *      is temporary, and focus will be abandonned shortly. Examples of transient requests are
     *      for the playback of driving directions, or notifications sounds.
     *      Use {@link #AUDIOFOCUS_GAIN_TRANSIENT_MAY_DUCK} to indicate also that it's ok for
     *      the previous focus owner to keep playing if it ducks its audio output.
     *      Alternatively use {@link #AUDIOFOCUS_GAIN_TRANSIENT_EXCLUSIVE} for a temporary request
     *      that benefits from the system not playing disruptive sounds like notifications, for
     *      usecases such as voice memo recording, or speech recognition.
     *      Use {@link #AUDIOFOCUS_GAIN} for a focus request of unknown duration such
     *      as the playback of a song or a video.
     *  @return {@link #AUDIOFOCUS_REQUEST_FAILED} or {@link #AUDIOFOCUS_REQUEST_GRANTED}
     */
    public int requestAudioFocus(OnAudioFocusChangeListener l, int streamType, int durationHint)
下面几个参数都是和onAudioFocusChange(int focusChange)中的focusChange参数对应的

AUDIOFOCUS_GAIN_TRANSIENT：获取的短暂的焦点，就是告知被剥夺者，你很快会重获焦点。对应AUDIOFOCUS_LOSS_TRANSIENT

AUDIOFOCUS_GAIN_TRANSIENT_MAY_DUCK：获取焦点，告知被剥夺者，你可以继续播放并将音量降为0或者低音量播放。对应AUDIOFOCUS_LOSS_TRANSIENT_CAN_DUCK

AUDIOFOCUS_GAIN_TRANSIENT_EXCLUSIVE：获取短暂焦点，但非常期望没有其他声音在播放。这个没有对应的loss标志。

AUDIOFOCUS_GAIN：获取较长期的焦点，对应AUDIOFOCUS_LOSS；



下面是其他博客的解释，但是我觉得是错误的，AUDIOFOCUS_LOSS不是失去很长时间，而是在request的时候参数是AUDIOFOCUS_GAIN，而AUDIOFOCUS_LOSS的解释是

失去焦点的时间未知，可能会长时间失去焦点。

focusChange参数告你音频焦点时如何改变的，并且能够是下面的值之一（它们是所有的在AudioManager类中定义的常量）：

    AUDIOFOCUS_GAIN&#

本文标签： 音频焦点

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