Android FrameWork音频管理AudioManager的一点解析(续一)

           上篇里面提到了声音调整的两种操作，接下来就要具体分析下音量调节的大概步骤,分别涉及到两部分:

           android\frameworks\base\media\java\android\media\AudioService.java

           android\frameworks\base\media\java\android\media\IAudioService.aidl

           其中adjustStreamVolume(int streamType, int direction, int flags)函数的声明是在AudioService.aidl中，而函数的实现是在AudioService.java中。

          下面具体可以看源码:

    /** @see AudioManager#adjustStreamVolume(int, int, int) */
    public void adjustStreamVolume(int streamType, int direction, int flags) {
        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);
        // get last audible index if stream is muted, current index otherwise
        final int aliasIndex = streamState.getIndex(device,
                                                  (streamState.muteCount() != 0) /* lastAudible */);
        boolean adjustVolume = true;

        // convert one UI step (+/-1) into a number of internal units on the stream alias
        int 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);
            if ((streamTypeAlias == getMasterStreamType()) &&
                    (mRingerMode == AudioManager.RINGER_MODE_SILENT)) {
                streamState.setLastAudibleIndex(0, device);
            }
        }

        // If stream is muted, adjust last audible index only
        int index;
        final int oldIndex = mStreamStates[streamType].getIndex(device,
                (mStreamStates[streamType].muteCount() != 0) /* lastAudible */);

        if (streamState.muteCount() != 0) {
            if (adjustVolume) {
                // Post a persist volume msg
                // no need to persist volume on all streams sharing the same alias
                streamState.adjustLastAudibleIndex(direction * step, device);
                sendMsg(mAudioHandler,
                        MSG_PERSIST_VOLUME,
                        SENDMSG_QUEUE,
                       PERSIST_LAST_AUDIBLE,
                        device,
                        streamState,
                        PERSIST_DELAY);
            }
            index = mStreamStates[streamType].getIndex(device, true  /* lastAudible */);
        } else {
            if (adjustVolume && streamState.adjustIndex(direction * step, device)) {
                // 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);
            }
            index = mStreamStates[streamType].getIndex(device, false  /* lastAudible */);
        }

        sendVolumeUpdate(streamType, oldIndex, index, flags);
    }

    private void ensureValidDirection(int direction) {
        if (direction < AudioManager.ADJUST_LOWER || direction > AudioManager.ADJUST_RAISE) {
            throw new IllegalArgumentException("Bad direction " + direction);
        }
    }

    private void ensureValidSteps(int steps) {
        if (Math.abs(steps) > MAX_BATCH_VOLUME_ADJUST_STEPS) {
            throw new IllegalArgumentException("Bad volume adjust steps " + steps);
        }
    }

    private void ensureValidStreamType(int streamType) {
        if (streamType < 0 || streamType >= mStreamStates.length) {
            throw new IllegalArgumentException("Bad stream type " + streamType);
        }
    }

        int step = rescaleIndex(10, streamType, streamTypeAlias);

        此参数为调整步进数值的

        再下面的判断条件if (streamState.muteCount() != 0)为判断是否是从静音状态发起的音量调整以便进行不同的操作。

        在函数的最后

        sendVolumeUpdate(streamType, oldIndex, index, flags);

        此函数则是用于更新系统音量条的显示

    // UI update and Broadcast Intent
    private void sendVolumeUpdate(int streamType, int oldIndex, int index, int flags) {
        if (!mVoiceCapable && (streamType == AudioSystem.STREAM_RING)) {
            streamType = AudioSystem.STREAM_NOTIFICATION;
        }

        mVolumePanel.postVolumeChanged(streamType, flags);

        oldIndex = (oldIndex + 5) / 10;
        index = (index + 5) / 10;
        Intent intent = new Intent(AudioManager.VOLUME_CHANGED_ACTION);
        if (streamType == AudioManager.STREAM_VOICE_CALL)
        	streamType = AudioManager.STREAM_MUSIC;
        intent.putExtra(AudioManager.EXTRA_VOLUME_STREAM_TYPE, streamType);
        intent.putExtra(AudioManager.EXTRA_VOLUME_STREAM_VALUE, index);
        intent.putExtra(AudioManager.EXTRA_PREV_VOLUME_STREAM_VALUE, oldIndex);
        mContext.sendBroadcast(intent);
    }

        \android\frameworks\base\core\java\android\view\VolumePanel.java

       其中VolumePanel.java则用于显示系统音量条的显示，其中具体如何显示可以参考代码。同时此部分代码中会涉及到系统所有音量相关的图标显示，需要进行修改美化等操作的可以具体找到资源文件进行修改。

      具体路径可以在

      android\frameworks\base\core\res\res

     另一种设置音量的方法setStreamVolume(int streamType, int index, int flags)也是同样的可以在上述代码中找到，关于音量调整的部分解析到此基本结束，暂时可以明白的就上述的流程了。