Android Audio音量——硬按键调节音量（七）
前面的文章已经介绍了音量调整及静音设置的相关调用，这里我们来梳理一下通过硬按键来调节音量及静音的相关调用流程。
一、硬按键调用
这里我们从 PhoneWindowManager 开始，该类主要负责管理设备上的所有窗口，包括应用程序窗口和其他系统窗口。同时负责输入事件的分发工作，包括我们这里要分析的硬按键事件。
1、PhoneWindowManager
源码位置：/frameworks/base/services/core/java/com/android/server/policy/PhoneWindowManager.java
interceptKeyBeforeDispatching
@Override
public long interceptKeyBeforeDispatching(IBinder focusedToken, KeyEvent event, int policyFlags) {final int keyCode = event.getKeyCode();……if (keyCode == KeyEvent.KEYCODE_VOLUME_UP || keyCode == KeyEvent.KEYCODE_VOLUME_DOWN|| keyCode == KeyEvent.KEYCODE_VOLUME_MUTE) {if (mUseTvRouting || mHandleVolumeKeysInWM) {dispatchDirectAudioEvent(event);return -1;}……}……
}该函数在按键事件被分发给应用程序之前进行拦截和处理，也就是来处理音量键的按下事件。这里调用了 dispatchDirectAudioEvent() 函数。
dispatchDirectAudioEvent
private void dispatchDirectAudioEvent(KeyEvent event) {// 通过 HDMI 音频系统客户端发送按键事件（这里不关注）……try {// 处理按键事件getAudioService().handleVolumeKey(event, mUseTvRouting, mContext.getOpPackageName(), TAG);} catch (Exception e) {……}
}static IAudioService getAudioService() {IAudioService audioService = IAudioService.Stub.asInterface(ServiceManager.checkService(Context.AUDIO_SERVICE));if (audioService == null) {Log.w(TAG, "Unable to find IAudioService interface.");}return audioService;
}这里主要负责处理直接与音频相关的按键事件，最终调用 AudioService 中的 handleVolumeKey() 函数。
2、AudioService
源码位置：/frameworks/base/services/core/java/com/android/server/audio/AudioService.java
handleVolumeKey
public void handleVolumeKey(@NonNull KeyEvent event, boolean isOnTv, @NonNull String callingPackage, @NonNull String caller) {int keyEventMode = VOL_ADJUST_NORMAL;……int flags = AudioManager.FLAG_SHOW_UI | AudioManager.FLAG_PLAY_SOUND | AudioManager.FLAG_FROM_KEY;switch (event.getKeyCode()) {case KeyEvent.KEYCODE_VOLUME_UP: // 音量上adjustSuggestedStreamVolume(AudioManager.ADJUST_RAISE,AudioManager.USE_DEFAULT_STREAM_TYPE, flags, callingPackage, caller, Binder.getCallingUid(), true, keyEventMode);break;case KeyEvent.KEYCODE_VOLUME_DOWN: // 音量下adjustSuggestedStreamVolume(AudioManager.ADJUST_LOWER,AudioManager.USE_DEFAULT_STREAM_TYPE, flags, callingPackage, caller,Binder.getCallingUid(), true, keyEventMode);break;case KeyEvent.KEYCODE_VOLUME_MUTE: // 静音if (event.getAction() == KeyEvent.ACTION_DOWN && event.getRepeatCount() == 0) {adjustSuggestedStreamVolume(AudioManager.ADJUST_TOGGLE_MUTE,AudioManager.USE_DEFAULT_STREAM_TYPE, flags, callingPackage, caller,Binder.getCallingUid(), true, VOL_ADJUST_NORMAL);}break;……}
}可以看到，这里对于音量上、音量下和静音的硬按键处理都是调用 adjustSuggestedStreamVolume() 函数继续处理。
adjustSuggestedStreamVolume
public void adjustSuggestedStreamVolume(int direction, int suggestedStreamType, int flags,String callingPackage, String caller) {// 检查调用者是否有 MODIFY_AUDIO_SETTINGS 权限boolean hasModifyAudioSettings = mContext.checkCallingPermission(Manifest.permission.MODIFY_AUDIO_SETTINGS)== PackageManager.PERMISSION_GRANTED;adjustSuggestedStreamVolume(direction, suggestedStreamType, flags, callingPackage,caller, Binder.getCallingUid(), hasModifyAudioSettings, VOL_ADJUST_NORMAL);
}private void adjustSuggestedStreamVolume(int direction, int suggestedStreamType, int flags,String callingPackage, String caller, int uid, boolean hasModifyAudioSettings, int keyEventMode) {……// 通知外部音量控制器boolean hasExternalVolumeController = notifyExternalVolumeController(direction);……// 调整音量adjustStreamVolume(streamType, direction, flags, callingPackage, caller, uid, hasModifyAudioSettings, keyEventMode);
}对于音量的调整，我们在前面的文章中已经分析过了，这里就不再重复。这里我们主要看 notifyExternalVolumeController()，该函数其实就是相当于一个回调函数，用来通知外部音量控制器的操作。
notifyExternalVolumeController
private boolean notifyExternalVolumeController(int direction) {final IAudioPolicyCallback externalVolumeController;……sendMsg(mAudioHandler, MSG_NOTIFY_VOL_EVENT, SENDMSG_QUEUE, direction, 0 /*ignored*/,externalVolumeController, 0 /*delay*/);return true;
}这里通过发送消息的方式告知外部控制器音量调整的方向。
onNotifyVolumeEvent
private class AudioHandler extends Handler {……private void onNotifyVolumeEvent(@NonNull IAudioPolicyCallback apc, @AudioManager.VolumeAdjustment int direction) {try {apc.notifyVolumeAdjust(direction);} catch(Exception e) {}}……@Overridepublic void handleMessage(Message msg) {switch (msg.what) {……case MSG_NOTIFY_VOL_EVENT:onNotifyVolumeEvent((IAudioPolicyCallback) msg.obj, msg.arg1);break;……}}
}这里首先对 MSG_NOTIFY_VOL_EVENT 消息进行了处理，调用了 onNotifyVolumeEvent() 函数。接着又调用了 IAudioPolicyCallback 的 notifyVolumeAdjust() 函数，这里一个 AIDL 接口，其实现在 AudioPolicy 中。
3、AudioPolicy
源码位置：/frameworks/base/media/java/android/media/audiopolicy/AudioPolicy.java
notifyVolumeAdjust
private final IAudioPolicyCallback mPolicyCb = new IAudioPolicyCallback.Stub() {public void notifyVolumeAdjust(int adjustment) {sendMsg(MSG_VOL_ADJUST, null /* ignored */, adjustment);……}
};这里发送一个 MSG_VOL_ADJUST 用来处理音量相关的回调。
private final static int MSG_VOL_ADJUST = 6;private class EventHandler extends Handler {…… @Overridepublic void handleMessage(Message msg) {switch(msg.what) {// 焦点状态……case MSG_VOL_ADJUST:if (mVolCb != null) {mVolCb.onVolumeAdjustment(msg.arg1);}break;……}}
}这里除了处理硬按键调整音量外，还有焦点状态相关的处理，这里我们不去关注。我们先来看一下 mVolCb 参数。
setAudioPolicyVolumeCallback
public static class Builder {private AudioPolicyVolumeCallback mVolCb;@NonNullpublic Builder setAudioPolicyVolumeCallback(@NonNull AudioPolicyVolumeCallback vc) {……mVolCb = vc;return this;}……
}public static abstract class AudioPolicyVolumeCallback {public AudioPolicyVolumeCallback() {}/*** 当按下按键事件触发音量键相关更改时调用* @param adjustment 键的音量调节类型*/public void onVolumeAdjustment(@AudioManager.VolumeAdjustment int adjustment) {}
}可以看到 mVolCb 其实就是通过 Builder 中的 setAudioPolicyVolumeCallback() 函数设置进来的一个 AudioPolicyVolumeCallback 回调，下面就来看一下该回调的监听。
4、CarAudioService
不难发现，在 CarAudioService 中的 init() 中调用了 setupDynamicRoutingLocked() 函数，该函数中设置了 AudioPolicyVolumeCallback 回调监听。
源码位置：/packages/services/Car/service/src/com/android/car/audio/CarAudioService.java
setupDynamicRoutingLocked
private void setupDynamicRoutingLocked() {final AudioPolicy.Builder builder = new AudioPolicy.Builder(mContext);……// Attach the {@link AudioPolicyVolumeCallback}builder.setAudioPolicyVolumeCallback(mAudioPolicyVolumeCallback);……
}下面来看一下监听函数的相关处理。
private final AudioPolicy.AudioPolicyVolumeCallback mAudioPolicyVolumeCallback =new AudioPolicy.AudioPolicyVolumeCallback() {@Overridepublic void onVolumeAdjustment(int adjustment) {int zoneId = CarAudioManager.PRIMARY_AUDIO_ZONE;// 获取音频上下文@AudioContext int suggestedContext = getSuggestedAudioContext();// 获取音量组 IDint groupId;synchronized (mImplLock) {groupId = getVolumeGroupIdForAudioContextLocked(zoneId, suggestedContext);}……// 获取当前音量final int currentVolume = getGroupVolume(zoneId, groupId);final int flags = AudioManager.FLAG_FROM_KEY | AudioManager.FLAG_SHOW_UI;// 处理不同的音量调整情况switch (adjustment) {case AudioManager.ADJUST_LOWER: // 降低音量int minValue = Math.max(currentVolume - 1, getGroupMinVolume(zoneId, groupId));setGroupVolume(zoneId, groupId, minValue , flags);break;case AudioManager.ADJUST_RAISE: // 提高音量int maxValue = Math.min(currentVolume + 1, getGroupMaxVolume(zoneId, groupId));setGroupVolume(zoneId, groupId, maxValue, flags);break;case AudioManager.ADJUST_MUTE: // 静音setMasterMute(true, flags);callbackMasterMuteChange(zoneId, flags);break;case AudioManager.ADJUST_UNMUTE: // 取消静音setMasterMute(false, flags);callbackMasterMuteChange(zoneId, flags);break;case AudioManager.ADJUST_TOGGLE_MUTE: // 切换静音状态setMasterMute(!mAudioManager.isMasterMute(), flags);callbackMasterMuteChange(zoneId, flags);break;case AudioManager.ADJUST_SAME:default:break;}}
};这里可以看到在静音状态改变后，调用 callbackMasterMuteChange 方法通知静音状态的变化，这与前面文章中静音设置中的回调函数相对应。