什么是SystemUI？简单分析

SystemUI概览

SystemUI属于系统级的apk，位置在frameworks\base\packages\SystemUI，主要功能有：

状态栏信息显示，比如电池，wifi信号，3G/4G等icon显示
通知面板，比如系统消息，第三方应用消息
近期任务栏显示面板，比如长按近期任务快捷键，显示近期使用的应用
截图服务
壁纸服务
……

SystemUI的启动流程

SystemServer启动后，会在Main Thread启动ActivityManagerService，当ActivityManagerService systemReady后，会去启动SystemUIService。
SystemServer路径:frameworks/base/services/java/com/android/server/SystemServer.java

mActivityManagerService.systemReady(new Runnable() {@Overridepublic void run() {Slog.i(TAG, "Making services ready");......Trace.traceBegin(Trace.TRACE_TAG_SYSTEM_SERVER, "StartSystemUI");try {startSystemUi(context);} catch (Throwable e) {reportWtf("starting System UI", e);}Trace.traceEnd(Trace.TRACE_TAG_SYSTEM_SERVER);......}            });

在这个方法里启动一个SystemUIService服务

static final void startSystemUi(Context context) {Intent intent = new Intent();intent.setComponent(new ComponentName("com.android.systemui", "com.android.systemui.SystemUIService"));intent.addFlags(Intent.FLAG_DEBUG_TRIAGED_MISSING);//Slog.d(TAG, "Starting service: " + intent);context.startServiceAsUser(intent, UserHandle.SYSTEM);
}

通过startServiceAsUser，SystemUIService就启动了，即SystemUI进程开机启动。

public class SystemUIService extends Service {@Overridepublic void onCreate() {super.onCreate();((SystemUIApplication) getApplication()).startServicesIfNeeded();}......

在SystemUIService的onCreate方法中会调用SystemUIApplication的startServicesIfNeeded方法，这个方法会调用 startServicesIfNeeded(SERVICES)方法启动一系列服务(并不是真正的service,都继承自SystemUI)。

public class SystemUIApplication extends Application {....../*** The classes of the stuff to start.*/private final Class<?>[] SERVICES = new Class[] {com.android.systemui.tuner.TunerService.class,com.android.systemui.keyguard.KeyguardViewMediator.class,com.android.systemui.recents.Recents.class,com.android.systemui.volume.VolumeUI.class,Divider.class,com.android.systemui.statusbar.SystemBars.class,com.android.systemui.usb.StorageNotification.class,com.android.systemui.power.PowerUI.class,com.android.systemui.media.RingtonePlayer.class,com.android.systemui.keyboard.KeyboardUI.class,com.android.systemui.tv.pip.PipUI.class,com.android.systemui.shortcut.ShortcutKeyDispatcher.class,com.android.systemui.VendorServices.class};......public void startServicesIfNeeded() {startServicesIfNeeded(SERVICES);}
}

所有SERVICES统一继承了SystemUI类：

public abstract class SystemUI {......public abstract void start();protected void onConfigurationChanged(Configuration newConfig) {}public void dump(FileDescriptor fd, PrintWriter pw, String[] args) {}protected void onBootCompleted() {}......
}

startServicesIfNeeded方法会遍历SERVICES 这个数组,依次调用service的start方法启动服务。

private void startServicesIfNeeded(Class<?>[] services) {......final int N = services.length;for (int i=0; i<N; i++) {Class<?> cl = services[i];if (DEBUG) Log.d(TAG, "loading: " + cl);try {Object newService = SystemUIFactory.getInstance().createInstance(cl);mServices[i] = (SystemUI) ((newService == null) ? cl.newInstance() : newService);} catch (IllegalAccessException ex) {throw new RuntimeException(ex);} catch (InstantiationException ex) {throw new RuntimeException(ex);}mServices[i].mContext = this;mServices[i].mComponents = mComponents;if (DEBUG) Log.d(TAG, "running: " + mServices[i]);mServices[i].start();if (mBootCompleted) {mServices[i].onBootCompleted();}}......
}

状态栏

状态栏（SystemBars）service是SystemUI中最重要的service，代码量最多，最复杂的，界面结构也复杂。根据前面的内容可知，启动SystemBars是通过调用start()方法，如下图：

    public void start() {if (DEBUG) Log.d(TAG, "start");mServiceMonitor = new ServiceMonitor(TAG, DEBUG,mContext, Settings.Secure.BAR_SERVICE_COMPONENT, this);mServiceMonitor.start();  // will call onNoService if no remote service is found}

这里实质是回调到到SystemBars的onNoService()方法，最后是调用SystemBars的createStatusBarFromConfig()方法：

    private void createStatusBarFromConfig() {......String clsName = mContext.getString(R.string.config_statusBarComponent);......try {cls = mContext.getClassLoader().loadClass(clsName);} catch (Throwable t) {throw andLog("Error loading status bar component: " + clsName, t);}try {mStatusBar = (BaseStatusBar) cls.newInstance();} catch (Throwable t) {throw andLog("Error creating status bar component: " + clsName, t);}......mStatusBar.start();......}

上图可以看到，从string资源文件里面读取class name，通过java的映射机制实例化对象，然后调用start()方法启动，class name的值如下图：

    <!-- Component to be used as the status bar service.  Must implement the IStatusBarinterface.  This name is in the ComponentName flattened format (package/class)  --><string name="config_statusBarComponent" translatable="false">com.android.systemui.statusbar.phone.PhoneStatusBar</string>

该配置文件在SystemUI/res/values/config.xml中。所以实质是PhoneStatusBar调用了start()方法。
SystemBars模块的初始化过程主要涉及的类有：

SystemUI/src/com/android/systemui/statusbar/phone/PhoneStatusBar.java
SystemUI/src/com/android/systemui/statusbar/BaseStatusBar.java
SystemUI/src/com/android/systemui/statusbar/CommandQueue.java

PhoneStatusBar的父类是BaseStatusBar继承于SystemUI，SystemBars调用PhoneStatusBar中的start()方法，类关系图如下：

PhoneStatusBar的start()

public void start() {......super.start(); // calls createAndAddWindows()......addNavigationBar();......
}

如上图，调用父类中的start()方法，即BaseStatsuBar中的start()方法。然后调用addNavigationBar()方法实例化导航条。状态栏的布局层次结构如下图：

继续看BaseStatsuBar中的方法。

public void start() {......mBarService = IStatusBarService.Stub.asInterface(ServiceManager.getService(Context.STATUS_BAR_SERVICE));......// Connect in to the status bar manager servicemCommandQueue = new CommandQueue(this);int[] switches = new int[9];ArrayList<IBinder> binders = new ArrayList<IBinder>();ArrayList<String> iconSlots = new ArrayList<>();ArrayList<StatusBarIcon> icons = new ArrayList<>();Rect fullscreenStackBounds = new Rect();Rect dockedStackBounds = new Rect();try {mBarService.registerStatusBar(mCommandQueue, iconSlots, icons, switches, binders,fullscreenStackBounds, dockedStackBounds);} catch (RemoteException ex) {// If the system process isn't there we're doomed anyway.}createAndAddWindows();......// Set up the initial icon stateint N = iconSlots.size();int viewIndex = 0;for (int i=0; i < N; i++) {setIcon(iconSlots.get(i), icons.get(i));}// Set up the initial notification state.try {mNotificationListener.registerAsSystemService(mContext,new ComponentName(mContext.getPackageName(), getClass().getCanonicalName()),UserHandle.USER_ALL);} catch (RemoteException e) {Log.e(TAG, "Unable to register notification listener", e);}......
}

如上面BaseStatsuBar中的start()方法，实例化一些对象，此处的对象都是“空值”，然后通过IStatusBarService的实例mBarService对象注册到StatusBarManagerService。

mCommandQueue是CommandQueue的实例，在StatusBarManagerService的远程回调，实现StatusBarManagerService和SystemUI的通信。

然后调用createAndAddWindows()方法，该方法初始化status bar，notification，quick settings等的View控件。

在这里，还需要注意NotificationListenerService的实例mNotificationListener的registerAsSystemService()方法，该方法主要实现StatusBarManagerService和SystemUI的notification的控制通道，也就是说，StatusBarManagerService收到notification变化时，通过此通道通知SystemUI显示notification的变化。

通知显示过程

一个APP需要显示notification首先需要实例化一个NotificationManager的对象，然后调用NotificationManager的方法notify（）方法把创建好的Notification对象作为参数传进去。

public void notify(int id, Notification notification){notify(null, id, notification);
}

public void notify(String tag, int id, Notification notification){notifyAsUser(tag, id, notification, new UserHandle(UserHandle.myUserId()));
}

public void notifyAsUser(String tag, int id, Notification notification, UserHandle user){......INotificationManager service = getService();......try {service.enqueueNotificationWithTag(pkg, mContext.getOpPackageName(), tag, id,copy, idOut, user.getIdentifier());......} catch (RemoteException e) {throw e.rethrowFromSystemServer();}
}

上图中可以看到一个service的对象调用了enqueueNotificationWithTag()方法，该方法实质是远程调用NotificationManagerService中的enqueueNotificationWithTag()方法，该方法又直接调用enqueueNotificationInternal()，该方法如下：

void enqueueNotificationInternal(final String pkg, final String opPkg, final int callingUid,final int callingPid, final String tag, final int id, final Notification notification,int[] idOut, int incomingUserId) {......final StatusBarNotification n = new StatusBarNotification(pkg, opPkg, id, tag, callingUid, callingPid, 0, notification,user);......final NotificationRecord r = new NotificationRecord(getContext(), n);mHandler.post(new EnqueueNotificationRunnable(userId, r));......
}

这里会把NotificationManager传递过来的Notification对象进行很多处理，比如变换成NotificationRecord，实质就是把Notification缓存下来。在上图的这个过程，还有一些其它的处理逻辑，在这里就不详细说明。最后把这个NotificationRecord传递给EnqueueNotificationRunnable线程来处理：

    private class EnqueueNotificationRunnable implements Runnable {private final NotificationRecord r;private final int userId;EnqueueNotificationRunnable(int userId, NotificationRecord r) {this.userId = userId;this.r = r;};@Overridepublic void run() {synchronized (mNotificationList) {final StatusBarNotification n = r.sbn;......if (notification.getSmallIcon() != null) {StatusBarNotification oldSbn = (old != null) ? old.sbn : null;mListeners.notifyPostedLocked(n, oldSbn);} else {......}buzzBeepBlinkLocked(r);}}}

代码的末尾调用了buzzBeepBlinkLocked()方法，该方法主要处理Notification的声音和震动的逻辑。mListeners调用了notifyPostedLocked()方法，此方法最终会执行到如下图的代码：

private void notifyPosted(final ManagedServiceInfo info,final StatusBarNotification sbn, NotificationRankingUpdate rankingUpdate) {final INotificationListener listener = (INotificationListener)info.service;StatusBarNotificationHolder sbnHolder = new StatusBarNotificationHolder(sbn);try {listener.onNotificationPosted(sbnHolder, rankingUpdate);} catch (RemoteException ex) {Log.e(TAG, "unable to notify listener (posted): " + listener, ex);}
}

info.service返回一个INotificationListener的实例对象，该对象在上文中的mNotificationListener.registerAsSystemService()方法进行设置，所以listener.onNotificationPosted()方法实质是远程回调SystemUI中的方法:

private final NotificationListenerService mNotificationListener =new NotificationListenerService() {......@Overridepublic void onNotificationPosted(final StatusBarNotification sbn,final RankingMap rankingMap) {......if (sbn != null) {mHandler.post(new Runnable() {@Overridepublic void run() {......if (isUpdate) {updateNotification(sbn, rankingMap);} else {addNotification(sbn, rankingMap, null /* oldEntry */);}}});}}
}

代码运行又回到了BaseStatusBar.java类中，从APP调用NotificationManager的notify()方法到BaseStatusBar的addNotification()或updateNotification()方法，经历了一个复杂的过程。就不再往下详情说明Notification到达SystemUI的处理过程了，之后有机会我们继续分析。

锁屏

锁屏（Keyguard）service在SystemUI是一个比较特殊的模块，特殊在于SystemUI启动的service只是一个信息传递者，也就是KeyguardViewMediator，并没有做锁屏或解屏的实质操作。在这里，涉及到三个比较关键的类是：

SystemUI/src/com/android/systemui/keyguard/KeyguardViewMediator.java
SystemUI/src/com/android/systemui/keyguard/KeyguardService.java
Keyguard/src/com/android/keyguard/KeyguardUpdateMonitor.java

KeyguardViewMediator和KeyguardService在源码中位于SystemUI中，而KeyguardUpdateMonitor则位于KeyGuard中。在KeyguardViewMediator的初始化中主要做了三件事，如图：

public void start() {synchronized (this) {setupLocked();}putComponent(KeyguardViewMediator.class, this);
}

private void setupLocked() {......mUpdateMonitor = KeyguardUpdateMonitor.getInstance(mContext);......mStatusBarKeyguardViewManager =SystemUIFactory.getInstance().createStatusBarKeyguardViewManager(mContext,mViewMediatorCallback, mLockPatternUtils);final ContentResolver cr = mContext.getContentResolver();mDeviceInteractive = mPM.isInteractive();......if (soundPath != null) {mLockSoundId = mLockSounds.load(soundPath, 1);}if (soundPath == null || mLockSoundId == 0) {Log.w(TAG, "failed to load lock sound from " + soundPath);}soundPath = Settings.Global.getString(cr, Settings.Global.UNLOCK_SOUND);if (soundPath != null) {mUnlockSoundId = mLockSounds.load(soundPath, 1);}if (soundPath == null || mUnlockSoundId == 0) {Log.w(TAG, "failed to load unlock sound from " + soundPath);}soundPath = Settings.Global.getString(cr, Settings.Global.TRUSTED_SOUND);if (soundPath != null) {mTrustedSoundId = mLockSounds.load(soundPath, 1);}if (soundPath == null || mTrustedSoundId == 0) {Log.w(TAG, "failed to load trusted sound from " + soundPath);}......
}

实例化KeyguardUpdateMonitor的实例mUpdateMonitor，KeyguardUpdateMonitor负责更新已经锁屏界面上的内容（如时间）。当然，KeyguardUpdateMonitor只是一个信息传递者，实际去刷新界面的是StatusBar模块。Keyguard模块通知StatusBar刷新解密是通过KeyguardUpdateMonitorCallback这个类进行远程回调，该类的实例在StatusBar模块启动时通过KeyguardService获取到IKeyguardService的远端实例，通过IKeyguardService远程调用IKeyguardService的addStateMonitorCallback()方法实例化KeyguardUpdateMonitorCallback对象，SystemUI/src/com/android/systemui/keyguard/KeyguardService.java

private final IKeyguardService.Stub mBinder = new IKeyguardService.Stub() {@Override // Binder interfacepublic void addStateMonitorCallback(IKeyguardStateCallback callback) {checkPermission();mKeyguardViewMediator.addStateMonitorCallback(callback);}......@Override // Binder interfacepublic void onScreenTurnedOn() {Trace.beginSection("KeyguardService.mBinder#onScreenTurningOn");checkPermission();mKeyguardViewMediator.onScreenTurnedOn();Trace.endSection();}......
};

SystemUI启动的Keyguard模块并没有真正的去操作锁屏界面，而是作为一个信息传递者把信息传递给StatusBar模块。
KeyguardService在KeyguardServiceDelegate中绑定调用。
frameworks/base/services/core/java/com/android/server/policy/keyguard/KeyguardServiceDelegate.java:

public void bindService(Context context) {Intent intent = new Intent();final Resources resources = context.getApplicationContext().getResources();final ComponentName keyguardComponent = ComponentName.unflattenFromString(resources.getString(com.android.internal.R.string.config_keyguardComponent));intent.addFlags(Intent.FLAG_DEBUG_TRIAGED_MISSING);intent.setComponent(keyguardComponent);boolean isBox = isBox();if (isBox || !context.bindServiceAsUser(intent, mKeyguardConnection,Context.BIND_AUTO_CREATE, mScrimHandler, UserHandle.SYSTEM)) {Log.v(TAG, "*** Keyguard: can't bind to " + keyguardComponent);mKeyguardState.showing = false;mKeyguardState.showingAndNotOccluded = false;mKeyguardState.secure = false;synchronized (mKeyguardState) {// TODO: Fix synchronisation model in this class. The other state in this class// is at least self-healing but a race condition here can lead to the scrim being// stuck on keyguard-less devices.mKeyguardState.deviceHasKeyguard = false;hideScrim();}} else {if (DEBUG) Log.v(TAG, "*** Keyguard started");}
}private final ServiceConnection mKeyguardConnection = new ServiceConnection() {@Overridepublic void onServiceConnected(ComponentName name, IBinder service) {if (DEBUG) Log.v(TAG, "*** Keyguard connected (yay!)");mKeyguardService = new KeyguardServiceWrapper(mContext,IKeyguardService.Stub.asInterface(service), mShowingStateChangedCallback);if (mKeyguardState.systemIsReady) {// If the system is ready, it means keyguard crashed and restarted.mKeyguardService.onSystemReady();if (mKeyguardState.currentUser != UserHandle.USER_NULL) {// There has been a user switch earliermKeyguardService.setCurrentUser(mKeyguardState.currentUser);}// This is used to hide the scrim once keyguard displays.if (mKeyguardState.interactiveState == INTERACTIVE_STATE_AWAKE) {mKeyguardService.onStartedWakingUp();}if (mKeyguardState.screenState == SCREEN_STATE_ON|| mKeyguardState.screenState == SCREEN_STATE_TURNING_ON) {mKeyguardService.onScreenTurningOn(new KeyguardShowDelegate(mDrawnListenerWhenConnect));}if (mKeyguardState.screenState == SCREEN_STATE_ON) {mKeyguardService.onScreenTurnedOn();}mDrawnListenerWhenConnect = null;}if (mKeyguardState.bootCompleted) {mKeyguardService.onBootCompleted();}if (mKeyguardState.occluded) {mKeyguardService.setOccluded(mKeyguardState.occluded, false /* animate */);}}@Overridepublic void onServiceDisconnected(ComponentName name) {if (DEBUG) Log.v(TAG, "*** Keyguard disconnected (boo!)");mKeyguardService = null;}};

com.android.internal.R.string.config_keyguardComponent的默认配置值：

<!-- Keyguard component -->
<string name="config_keyguardComponent" translatable="false">com.android.systemui/com.android.systemui.keyguard.KeyguardService</string>

KeyguardViewMediator启动的流程图如下：

总结

先大概看一遍流程，这个apk比较复杂，之后还会分析。