最近在学习并接触SystemUI模块的工作，Keyguard做为引入库也纳入了SystemUI的大家庭，所以整体感觉SystemUI模块还是挺大的，为了日后的查阅还是要写一下笔记。笔记记录过程中参考了许多网友的文章，在本文最后的文章参考会一一罗列，在此非常感谢他们的分享。
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:/base/services/java/com/android/server/SystemServer.java
mActivityManagerService.systemReady(newRunnable() {@Overridepublicvoidrun() { 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); ...... } });
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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);}
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通过startServiceAsUser，SystemUIService就启动了，即SystemUI进程开机启动。
publicclassSystemUIServiceextendsService{@OverridepublicvoidonCreate() {super.onCreate(); ((SystemUIApplication) getApplication()).startServicesIfNeeded(); } ......
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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);}}
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startServicesIfNeeded方法会遍历SERVICES 这个数组,依次调用service的start方法启动服务。
privatevoidstartServicesIfNeeded(Class[] services) {if(mServicesStarted) {return; }if(!mBootCompleted) {// check to see if maybe it was already completed long before we began// see ActivityManagerService.finishBooting()if("1".equals(SystemProperties.get("sys.boot_completed"))) { mBootCompleted =true;if(DEBUG) Log.v(TAG,"BOOT_COMPLETED was already sent"); } } Log.v(TAG,"Starting SystemUI services for user "+ Process.myUserHandle().getIdentifier() +"."); finalintN = services.length;for(inti=0; i 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) {thrownewRuntimeException(ex); }catch(InstantiationException ex) {thrownewRuntimeException(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(); } } mServicesStarted =true; }
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看到这里，这么多文字可能不够直观，那就看看图吧，非常感谢参考文章中的分享。
这里以SERVICES 中com.android.systemui.keyguard.KeyguardViewMediator.class为例，
SystemUI Services启动后，根据各Services的功能，SystemUI的各个模块就开始正常工作起来了。