Android 音量调节

音量调节在AudioService.java 的借口函数是 adjustStreamVolume 如下:

public void adjustStreamVolume(int streamType, int direction, int flags,
            String callingPackage) {
        if (mUseFixedVolume) {
            return;
        }
        if (DEBUG_VOL) Log.d(TAG, "adjustStreamVolume() stream="+streamType+", dir="+direction);

        ensureValidDirection(direction);
        ensureValidStreamType(streamType);

        // use stream type alias here so that streams with same alias have the same behavior,
        // including with regard to silent mode control (e.g the use of STREAM_RING below and in
        // checkForRingerModeChange() in place of STREAM_RING or STREAM_NOTIFICATION)
        int streamTypeAlias = mStreamVolumeAlias[streamType];
        VolumeStreamState streamState = mStreamStates[streamTypeAlias];

        final int device = getDeviceForStream(streamTypeAlias);

        int aliasIndex = streamState.getIndex(device);
        boolean adjustVolume = true;
        int step;

        // skip a2dp absolute volume control request when the device
        // is not an a2dp device
        if ((device & AudioSystem.DEVICE_OUT_ALL_A2DP) == 0 &&
            (flags & AudioManager.FLAG_BLUETOOTH_ABS_VOLUME) != 0) {
            return;
        }

        if (mAppOps.noteOp(STEAM_VOLUME_OPS[streamTypeAlias], Binder.getCallingUid(),
                callingPackage) != AppOpsManager.MODE_ALLOWED) {
            return;
        }

        // reset any pending volume command
        synchronized (mSafeMediaVolumeState) {
            mPendingVolumeCommand = null;
        }

        flags &= ~AudioManager.FLAG_FIXED_VOLUME;
        if ((streamTypeAlias == AudioSystem.STREAM_MUSIC) &&
               ((device & mFixedVolumeDevices) != 0)) {
            flags |= AudioManager.FLAG_FIXED_VOLUME;

            // Always toggle between max safe volume and 0 for fixed volume devices where safe
            // volume is enforced, and max and 0 for the others.
            // This is simulated by stepping by the full allowed volume range
            if (mSafeMediaVolumeState == SAFE_MEDIA_VOLUME_ACTIVE &&
                    (device & mSafeMediaVolumeDevices) != 0) {
                step = mSafeMediaVolumeIndex;
            } else {
                step = streamState.getMaxIndex();
            }
            if (aliasIndex != 0) {
                aliasIndex = step;
            }
        } else {
            // convert one UI step (+/-1) into a number of internal units on the stream alias
            step = rescaleIndex(10, streamType, streamTypeAlias);
        }

        // If either the client forces allowing ringer modes for this adjustment,
        // or the stream type is one that is affected by ringer modes
        if (((flags & AudioManager.FLAG_ALLOW_RINGER_MODES) != 0) ||
                (streamTypeAlias == getMasterStreamType())) {
            int ringerMode = getRingerMode();
            // do not vibrate if already in vibrate mode
            if (ringerMode == AudioManager.RINGER_MODE_VIBRATE) {
                flags &= ~AudioManager.FLAG_VIBRATE;
            }
            // Check if the ringer mode changes with this volume adjustment. If
            // it does, it will handle adjusting the volume, so we won't below
            adjustVolume = checkForRingerModeChange(aliasIndex, direction, step);
        }

        int oldIndex = mStreamStates[streamType].getIndex(device);                                                 在同一种streamtype 下, 每一个设备都有自己的index

        if (adjustVolume && (direction != AudioManager.ADJUST_SAME)) {

            // Check if volume update should be send to AVRCP
            if (streamTypeAlias == AudioSystem.STREAM_MUSIC &&
                (device & AudioSystem.DEVICE_OUT_ALL_A2DP) != 0 &&
                (flags & AudioManager.FLAG_BLUETOOTH_ABS_VOLUME) == 0) {
                synchronized (mA2dpAvrcpLock) {
                    if (mA2dp != null && mAvrcpAbsVolSupported) {
                        mA2dp.adjustAvrcpAbsoluteVolume(direction);
                    }
                }
            }

            if ((direction == AudioManager.ADJUST_RAISE) &&
                    !checkSafeMediaVolume(streamTypeAlias, aliasIndex + step, device)) {
                Log.e(TAG, "adjustStreamVolume() safe volume index = "+oldIndex);
                mVolumePanel.postDisplaySafeVolumeWarning(flags);
            } else if (streamState.adjustIndex(direction * step, device)) {                                            每按一次volume键, 都会调整index , direction 为调整方向,  -1 是调低 ,  +1是调高
                // Post message to set system volume (it in turn will post a message
                // to persist). Do not change volume if stream is muted.
                sendMsg(mAudioHandler,
                        MSG_SET_DEVICE_VOLUME,                                                                                
                        SENDMSG_QUEUE,
                        device,
                        0,
                        streamState,
                        0);
            }
        }
        int index = mStreamStates[streamType].getIndex(device);                                                       在同一种streamtype 下, 每一个设备都有自己的index
        sendVolumeUpdate(streamType, oldIndex, index, flags);
    }

下面分析下这个函数, 主要就是

1. (红色标记部分) 按volume key 都会保存调整index

2. (蓝色标记部分) 根据这个index , 调用到handleMessage 函数中的setDeviceVolume函数, 然后去AudioPolicyManagerBase.cpp 计算音频曲线, 然后在AudioPolicyManagerBase.cpp 中调用 mpClientInterface->setStreamVolume 函数, 把音量设置到AudioFlinger 中去

3. (绿色标记部分) 根据当前case 的streamtype , 和oldindex , index 去更新应用的音量条显示

另外标记紫色的地方是对RINGER_MODE_NORMAL, RINGER_MODE_VIBRATE 和RINGER_MODE_SILENT 进行转换

如果当前case 下的streamTypeAlias 等于getMasterStreamType() , 就会调用checkForRingerModeChange 这个函数,如下

private boolean checkForRingerModeChange(int oldIndex, int direction,  int step) {
        boolean adjustVolumeIndex = true;
        int ringerMode = getRingerMode();

        switch (ringerMode) {
        case RINGER_MODE_NORMAL:
            if (direction == AudioManager.ADJUST_LOWER) {
                if (mHasVibrator) {
                    // "step" is the delta in internal index units corresponding to a
                    // change of 1 in UI index units.
                    // Because of rounding when rescaling from one stream index range to its alias
                    // index range, we cannot simply test oldIndex == step:
                    //   (step <= oldIndex < 2 * step) is equivalent to: (old UI index == 1)
                    if (step <= oldIndex && oldIndex < 2 * step) {
                        ringerMode = RINGER_MODE_VIBRATE;
                    }
                } else {
                    // (oldIndex < step) is equivalent to (old UI index == 0)
                    if ((oldIndex < step) && mPrevVolDirection != AudioManager.ADJUST_LOWER) {
                        ringerMode = RINGER_MODE_SILENT;
                    }
                }
            }
            break;
        case RINGER_MODE_VIBRATE:
            if (!mHasVibrator) {
                Log.e(TAG, "checkForRingerModeChange() current ringer mode is vibrate" +
                        "but no vibrator is present");
                break;
            }
            if ((direction == AudioManager.ADJUST_LOWER)) {
                if (mPrevVolDirection != AudioManager.ADJUST_LOWER) {
                    ringerMode = RINGER_MODE_SILENT;
                }
            } else if (direction == AudioManager.ADJUST_RAISE) {
                ringerMode = RINGER_MODE_NORMAL;
            }
            adjustVolumeIndex = false;
            break;
        case RINGER_MODE_SILENT:
            if (direction == AudioManager.ADJUST_RAISE) {
                if (mHasVibrator) {
                    ringerMode = RINGER_MODE_VIBRATE;
                } else {
                    ringerMode = RINGER_MODE_NORMAL;
                }
            }
            adjustVolumeIndex = false;
            break;
        default:
            Log.e(TAG, "checkForRingerModeChange() wrong ringer mode: "+ringerMode);
            break;
        }

        setRingerMode(ringerMode);

        mPrevVolDirection = direction;

        return adjustVolumeIndex;
    }

这个函数绿色标记的地方,是获得和设置Ringer mode .

红色标记的地方, 说明如果音量条调到最低的时候, 就可以转换成振动 , 再到静音了