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);    }

解析上面函数可知，函数最开始会有一个对于前两个参数有效性的检测，贴出具体的检测代码:

    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);        }    }

继续跟进源码，可以看到

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);    }

可以看到源码中调用了

\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。

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