使用蓝牙耳机通话时，禁止静音

当拨打电话，并且使用蓝牙耳机的情况下，如果调节音量键-，使STREAM_MUSIC音频流音量为0，会导致通话静音，即无法听到声音，因此需要，此条件下直接返回-1，对按键进行拦截处理，不再向下分发。

//frameworks\base\services\core\java\com\android\server\policy\PhoneWindowManager.java
    @Override
    public long interceptKeyBeforeDispatching(WindowState win, KeyEvent event, int policyFlags) {
        .......
        else if (keyCode == KeyEvent.KEYCODE_VOLUME_UP
                || keyCode == KeyEvent.KEYCODE_VOLUME_DOWN
                || keyCode == KeyEvent.KEYCODE_VOLUME_MUTE) {
            if(keyCode == KeyEvent.KEYCODE_VOLUME_DOWN && mTelecomManager.isInCall() && mAudioManager.getStreamVolume(AudioManager.STREAM_MUSIC) <= 1){
                return -1;
            }
           if (mUseTvRouting || mHandleVolumeKeysInWM) {
                // On TVs or when the configuration is enabled, volume keys never
                // go to the foreground app.
                dispatchDirectAudioEvent(event);
                return -1;
            }
.......

这里用mTelecomManager.isInCall()来判断是否为通话中。

然后，后续发现，还存在2种导致通话静音的情况。
1.使用蓝牙耳机按键
2.快速连按KEYCODE_VOLUME_DOWN(音量－)

解决办法分别是在setStreamVolume和adjustSuggestedStreamVolume中添加return;的代码。

//frameworks\base\media\java\android\media\AudioManager.java
    public void setStreamVolume(int streamType, int index, int flags) {
        final IAudioService service = getService();
        Log.d(TAG, "setStreamVolume: StreamType = " + streamType + ", index = " + index + "， isInCall = " + mTelecomManager.isInCall());
        if ( mTelecomManager.isInCall() && streamType == STREAM_BLUETOOTH_SCO && index == 0){
            Log.d(TAG,"before return");
            return;
        }
        try {
            service.setStreamVolume(streamType, index, flags, getContext().getOpPackageName());
        } catch (RemoteException e) {
            throw e.rethrowFromSystemServer();
        }
    }

//frameworks\base\services\core\java\com\android\server\audio\AudioService.java
 private void adjustSuggestedStreamVolume(int direction, int suggestedStreamType, int flags,
            String callingPackage, String caller, int uid) {
        ........
        if (mTelecomManager.isInCall() && direction == AudioManager.ADJUST_LOWER && getStreamVolume(AudioSystem.STREAM_MUSIC) == 1){
            return;
        }
        ........
}

在快速按下音量-的时候，interceptKeyBeforeDispatching中的拦截失效了，看log可知，调用的是adjustSuggestedStreamVolume，因此在此处拦截。