Android系统音量条实例代码

  private enum StreamResources {
    BluetoothSCOStream(AudioManager.STREAM_BLUETOOTH_SCO,
        R.string.volume_icon_description_bluetooth,
        IC_AUDIO_BT,
        IC_AUDIO_BT_MUTE,
        false),
    // 这里省略了后面的几个枚举项的构造参数，这些与BluetoothSCOStream的内容是一致的
    RingerStream(...),
    VoiceStream(...),
    AlarmStream(...),
    MediaStream(...),
    NotificationStream(...),
    // for now, use media resources for master volume
    MasterStream(...),
    RemoteStream(...);// will be dynamically updated

    int streamType; // 流类型
    int descRes; // 描述信息
    int iconRes; // 图标
    int iconMuteRes; // 静音图标
    // RING, VOICE_CALL & BLUETOOTH_SCO are hidden unless explicitly requested
    boolean show; // 是否显示
    //构造函数
    StreamResources(int streamType, int descRes, int iconRes, int iconMuteRes, boolean show) {
      ...
    }
  }

  private static final StreamResources[] STREAMS = {
    StreamResources.BluetoothSCOStream,
    StreamResources.RingerStream,
    StreamResources.VoiceStream,
    StreamResources.MediaStream,
    StreamResources.NotificationStream,
    StreamResources.AlarmStream,
    StreamResources.MasterStream,
    StreamResources.RemoteStream
  };

  /** Object that contains data for each slider */
  private class StreamControl {
    int streamType;
    MediaController controller;
    ViewGroup group;
    ImageView icon;
    SeekBar seekbarView;
    TextView suppressorView;
    View divider;
    ImageView secondaryIcon;
    int iconRes;
    int iconMuteRes;
    int iconSuppressedRes;
  }

  private void createSliders() {
    ...
    // 遍历STREAM中所有的StreamResources实例
    for (int i = 0; i < STREAMS.length; i++) {
      StreamResources streamRes = STREAMS[i];
      final int streamType = streamRes.streamType;    
      ...
      final StreamControl sc = new StreamControl();// 为streamType创建一个StreamControl
      // 下面将初始化sc的成员变量
      ... 
      sc.seekbarView.setOnSeekBarChangeListener(mSeekListener); // 设置监听          
      mStreamControls.put(streamType, sc);// 将初始化好的sc放入mStreamControls中
    }
  }

  private final OnSeekBarChangeListener mSeekListener = new OnSeekBarChangeListener() {
    @Override
    public void onProgressChanged(SeekBar seekBar, int progress, boolean fromUser) {
      final Object tag = seekBar.getTag();
      if (fromUser && tag instanceof StreamControl) {
        StreamControl sc = (StreamControl) tag;
        //设置音量
        setStreamVolume(sc, progress,AudioManager.FLAG_SHOW_UI | AudioManager.FLAG_VIBRATE);        
      }
      resetTimeout();
    }
    ...
  };

    protected void onVolumeChanged(int streamType, int flags) {
    // 需要flags中包含AudioManager.FLAG_SHOW_UI 才会显示音量调节通知框
    if ((flags & AudioManager.FLAG_SHOW_UI) != 0) {
      synchronized (this) {
        if (mActiveStreamType != streamType) {
          reorderSliders(streamType); // 在Dialog里装载需要的StreamControl
        }
        onShowVolumeChanged(streamType, flags, null);
      }
    }
    // 是否播出Tone音，注意有个小延迟
    if ((flags & AudioManager.FLAG_PLAY_SOUND) != 0 && ! mRingIsSilent) {
      removeMessages(MSG_PLAY_SOUND);
      sendMessageDelayed(obtainMessage(MSG_PLAY_SOUND, streamType, flags), PLAY_SOUND_DELAY);
    }
    // 取消声音与振动的播放
    if ((flags & AudioManager.FLAG_REMOVE_SOUND_AND_VIBRATE) != 0) {
      removeMessages(MSG_PLAY_SOUND);
      removeMessages(MSG_VIBRATE);
      onStopSounds();
    }
    // 开始安排回收资源
    removeMessages(MSG_FREE_RESOURCES);
    sendMessageDelayed(obtainMessage(MSG_FREE_RESOURCES), FREE_DELAY);
    resetTimeout(); // 重置音量框超时关闭的时间
  }

  protected void onShowVolumeChanged(int streamType, int flags, MediaController controller) {
    int index = getStreamVolume(streamType);// 获取音量值
    int max = getStreamMaxVolume(streamType); // 获取音量最大值，这两个将用来设置进度条
    StreamControl sc = mStreamControls.get(streamType);
    //在这个switch语句中，我们要根据每种流类型的特点进行各种调整。例如Music有时就需要更新它的图标，因为使用蓝牙耳机时的图标和平时的不一样，所以每一次都需要更新一下
    switch (streamType) {
      case AudioManager.STREAM_MUSIC: {
        // Special case for when Bluetooth is active for music
        if ((mAudioManager.getDevicesForStream(AudioManager.STREAM_MUSIC) &
            (AudioManager.DEVICE_OUT_BLUETOOTH_A2DP |
            AudioManager.DEVICE_OUT_BLUETOOTH_A2DP_HEADPHONES |
            AudioManager.DEVICE_OUT_BLUETOOTH_A2DP_SPEAKER)) != 0) {
          setMusicIcon(IC_AUDIO_BT, IC_AUDIO_BT_MUTE);
        } else {
          setMusicIcon(IC_AUDIO_VOL, IC_AUDIO_VOL_MUTE);
        }
        break;
      }
      ...
    }

    if (sc != null) {
      ...
      updateSliderProgress(sc, index); // 更新Seekbar的显示
      final boolean muted = isMuted(streamType);
      updateSliderEnabled(sc, muted, (flags & AudioManager.FLAG_FIXED_VOLUME) != 0);
      ...
         updateSliderIcon(sc, muted); //更新stream_icon
      }
    }

    if (!isShowing()) { // 如果对话框还没有显示
      int stream = (streamType == STREAM_REMOTE_MUSIC) ? -1 : streamType;
      //一旦此通知框被显示，之后按下音量键都只能调节当前流类型的音量。直到通知框关闭时，重新调用forceVolumeControlStream(),并设置streamType为-1
      if (stream != STREAM_MASTER) {
        mAudioManager.forceVolumeControlStream(stream);
      }
      mDialog.show(); // 显示对话框
      ...
    }

    // Do a little vibrate if applicable (only when going into vibrate mode)
    if ((streamType != STREAM_REMOTE_MUSIC) &&
        ((flags & AudioManager.FLAG_VIBRATE) != 0) &&
        isNotificationOrRing(streamType) &&
        mAudioManager.getRingerModeInternal() == AudioManager.RINGER_MODE_VIBRATE) {
      sendMessageDelayed(obtainMessage(MSG_VIBRATE), VIBRATE_DELAY);//稍微振动（仅当进入振动模式时）
    }
  ...
  }

  private void updateSliderProgress(StreamControl sc, int progress) {
    final boolean isRinger = isNotificationOrRing(sc.streamType);
    if (isRinger && mAudioManager.getRingerModeInternal() == AudioManager.RINGER_MODE_SILENT) {
      progress = mLastRingerProgress;
    }
    if (progress < 0) {
      progress = getStreamVolume(sc.streamType); // 获取音量值
    }
    sc.seekbarView.setProgress(progress);//设置音量条
    if (isRinger) {
      mLastRingerProgress = progress;
    }
  }