Android 之 系统声音

Android的audio流的类型有以下12种：

 

/* The audio stream for phone calls */  
    public static final int STREAM_VOICE_CALL = 0;//通话连接时的音频流（通话声）  
    /* The audio stream for system sounds */  
    public static final int STREAM_SYSTEM = 1;//系统音频流  
    /* The audio stream for the phone ring and message alerts */  
    public static final int STREAM_RING = 2;//来电铃声  
    /* The audio stream for music playback */  
    public static final int STREAM_MUSIC = 3;//媒体音频流  
    /* The audio stream for alarms */  
    public static final int STREAM_ALARM = 4;//闹钟音频流  
    /* The audio stream for notifications */  
    public static final int STREAM_NOTIFICATION = 5;//通知音频流  
    /* @hide The audio stream for phone calls when connected on bluetooth */  
    public static final int STREAM_BLUETOOTH_SCO = 6;//从注释上看时使用蓝牙耳机通话的音频流  
    /* @hide The audio stream for enforced system sounds in certain countries (e.g camera in Japan) */  
    public static final int STREAM_SYSTEM_ENFORCED = 7;//一些国家强制使用的音频流？？不太明白  
    /* @hide The audio stream for DTMF tones */  
    public static final int STREAM_DTMF = 8;//DTMF音频流  
    /* @hide The audio stream for text to speech (TTS) */  
    public static final int STREAM_TTS = 9;//TTS: Text to Speech:文件到语言的音频流，即机器说话  
    /* @hide The audio stream for Fm */  
    public static final int STREAM_FM = 10;//FM的音频流  
    /* @hide The audio stream for MATV */  
    public static final int STREAM_MATV = 11;//TV的音频流 

每种音频流所规定的最大值：
/** @hide Maximum volume index values for audio streams */  
 private int[] MAX_STREAM_VOLUME = new int[] {  
     6,  // STREAM_VOICE_CALL  
     7,  // STREAM_SYSTEM  
     7,  // STREAM_RING  
     12, // STREAM_MUSIC  
     7,  // STREAM_ALARM  
     7,  // STREAM_NOTIFICATION  
     15, // STREAM_BLUETOOTH_SCO  
     7,  // STREAM_SYSTEM_ENFORCED  
     15, // STREAM_DTMF  
     15, // STREAM_TTS  
     13, //STREAM_FM  
     13  //stream_MATV  
 };  

 

public boolean performClick() {  
    sendAccessibilityEvent(AccessibilityEvent.TYPE_VIEW_CLICKED);  
  
    if (mOnClickListener != null) {  
        playSoundEffect(SoundEffectConstants.CLICK);  
        mOnClickListener.onClick(this);  
        return true;  
    }  
  
    return false;  
}  

从这里可以看到与用户接口onClickListener结合起来了，当用户注册了clickListener，则调用发出按键音函数playSoundEffect ()和响应用户写好的clickListener的onClick()方法。这里playSoundEffect函数传的参数SoundEffectContants.CLICK为多少呢，从SoundEffectConstants.java可知SoundEffectConstants.CLICK = 0: