【Android系统源码修改】如何修改frameworks实现音量统一调节

###1 修改音量最大值和默认音量

源码位置：frameworks/base/media/java/android/media/AudioService.java 约266行
MAX_STREAM_VOLUME为最大值，DEFAULT_STREAM_VOLUME为默认值
为了统一调节音量，把默认音量和最大音量，所有STREAM都保持一致。
如果采用Master音量调节，就不需要设置了，因为Master音量调节最大都是100

 /** @hide Maximum volume index values for audio streams */
   /// M: Modify the max stream volume @{
    private static final int[] MAX_STREAM_VOLUME = new int[] {
        20,  // STREAM_VOICE_CALL
        20,  // STREAM_SYSTEM
        20,  // STREAM_RING
        20,  // STREAM_MUSIC
        20,  // STREAM_ALARM
        20,  // STREAM_NOTIFICATION
        20,  // STREAM_BLUETOOTH_SCO
        20,  // STREAM_SYSTEM_ENFORCED
        20,  // STREAM_DTMF
        20,  // STREAM_TTS
    };
    /// @}

    /**
     * @hide Default volume index values for audio streams
     * M: modify the default stream volume @{
     */
    public static int[] DEFAULT_STREAM_VOLUME = new int[] {
        9,  // STREAM_VOICE_CALL
        9,  // STREAM_SYSTEM
        9,  // STREAM_RING
        9,  // STREAM_MUSIC
        9,  // STREAM_ALARM
        9,  // STREAM_NOTIFICATION
        9,  // STREAM_BLUETOOTH_SCO
        9,  // STREAM_SYSTEM_ENFORCED
        9,  // STREAM_DTMF
        9,  // STREAM_TTS
    };
    /** @ */

###2 拦截音量键分发

源码位置：frameworks/base/policy/src/com/android/internel/policy/impl/PhoneWindowManager.java 约2607行
方法名：public long interceptKeyBeforeDispatching(WindowState win, KeyEvent event, int policyFlags)
作用：在分发之前拦截按键事件。是否分发给应用自己处理，根据返回值：return -1 不返回，自己处理了。return 0 返回给应用自己处理

拦截音量键
音量键码：KeyEvent.KEYCODE_VOLUME_DOWN KeyEvent.KEYCODE_VOLUME_UP

if (keyCode == KeyEvent.KEYCODE_VOLUME_DOWN || keyCode == KeyEvent.KEYCODE_VOLUME_UP) {
     // TODO: 这里添加你需要音量键按下后做什么事
     return -1;
}

我们需要音量键按下后，发出按下广播。（来电铃声响起时，音量键起到静音作用，所以来电话的时候不拦截音量键，让系统处理）

Intent intent = new Intent();
intent.addFlags(Intent.FLAG_INCLUDE_STOPPED_PACKAGES);
if (keyCode == KeyEvent.KEYCODE_VOLUME_DOWN || keyCode == KeyEvent.KEYCODE_VOLUME_UP) {
    TelecomManager telecomManager = getTelecommService();
    if (telecomManager == null || !(telecomManager.isRinging() || telecomManager.isInCall())) {
        if (down) {
            if (keyCode == KeyEvent.KEYCODE_VOLUME_DOWN) {
                intent.setAction("xxx.ACTION_VOLUME_DOWN");
                mContext.sendBroadcast(intent);
            } else if (keyCode == KeyEvent.KEYCODE_VOLUME_UP) {
                intent.setAction("xxx.ACTION_VOLUME_UP");
                mContext.sendBroadcast(intent);
            }
            return -1;
        }
    }            
}

###3 在其他应用中添加广播接收者处理音量加减广播

public class VolumeEventReceiver extends BroadcastReceiver {
    Context mContext;
    AudioManager manager;
    int[] stream = {
            AudioManager.STREAM_RING,
            AudioManager.STREAM_ALARM,
            AudioManager.STREAM_NOTIFICATION,
            AudioManager.STREAM_DTMF,
            AudioManager.STREAM_VOICE_CALL,
            AudioManager.STREAM_SYSTEM,
            AudioManager.STREAM_MUSIC,
    };

    @Override
    public void onReceive(Context context, Intent intent) {
        try {
            mContext = context;
            manager = (AudioManager) mContext.getSystemService(Context.AUDIO_SERVICE);

            String action = intent.getAction();
            if ("xxx.ACTION_VOLUME_DOWN".equals(action)) {
                controlVolume(AudioManager.ADJUST_LOWER);

            } else if ("xxx.ACTION_VOLUME_UP".equals(action)) {
                controlVolume(AudioManager.ADJUST_RAISE);
            }

        } catch (Exception e) {
            Log.i("VolumeEvent", "*** Exception: " + e.getMessage());
        }
    }

    void controlVolume(int direction) {
        for (int i = 0; i < stream.length - 1; i++) {
            manager.adjustStreamVolume(stream[i], direction, 0);
        }
        // 显示媒体音量调节的图标，其他音量图标不显示
        manager.adjustStreamVolume(AudioManager.STREAM_MUSIC, direction,
                AudioManager.FLAG_SHOW_UI | AudioManager.FLAG_PLAY_SOUND);
    }

}

注册广播：

###4 打开主音量调节功能，设置音量加减步长

源码位置：frameworks/base/core/res/res/values/config.xml 约71行
将config_useMasterVolume设置为true。

true

约86行，第二个item根据调试设置步长。默认是5， 这里改成1。根据测试，调节音量时，从最小到最大，需要按+键16下左右

   0  1  

当用户调用adjustStreamVolume的时候，mUseMasterVolume是上面config_useMasterVolume的值。

public void adjustStreamVolume(int streamType, int direction, int flags) {
    IAudioService service = getService();
    Log.d(TAG, "adjustStreamVolume: StreamType = " + streamType + ", direction = " + direction);
    try {
        if (mUseMasterVolume) {
            service.adjustMasterVolume(direction, flags, mContext.getOpPackageName());
        } else {
            service.adjustStreamVolume(streamType, direction, flags,
                    mContext.getOpPackageName());
        }
    } catch (RemoteException e) {
        Log.e(TAG, "Dead object in adjustStreamVolume", e);
    }
}

由Master调节音量，所有音量最大为100，发出音量调节广播为：
"android.media.MASTER_VOLUME_CHANGED_ACTION"

而普通的音量调节，最大音量根据AudioService.java中MAX_STREAM_VOLUME定义的，默认音量DEFAULT_STREAM_VOLUME
广播为："android.media.VOLUME_CHANGED_ACTION"

###5 测试
写一个测试程序测试