1.从SystemServer启动

  private void run() {......// Start services.try {t.traceBegin("StartServices");startBootstrapServices(t);startCoreServices(t);startOtherServices(t);//从这里走startApexServices(t);// Only update the timeout after starting all the services so that we use// the default timeout to start system server.updateWatchdogTimeout(t);} catch (Throwable ex) {Slog.e("System", "******************************************");Slog.e("System", "************ Failure starting system services", ex);throw ex;} finally {t.traceEnd(); // StartServices}......

2.走startOtherServices()

/*** Starts a miscellaneous grab bag of stuff that has yet to be refactored and organized.*/private void startOtherServices(@NonNull TimingsTraceAndSlog t) {......t.traceBegin("StartSystemUI");try {startSystemUi(context, windowManagerF);} catch (Throwable e) {reportWtf("starting System UI", e);}......}

3.启动SystemUi

    private static void startSystemUi(Context context, WindowManagerService windowManager) {PackageManagerInternal pm = LocalServices.getService(PackageManagerInternal.class);Intent intent = new Intent();intent.setComponent(pm.getSystemUiServiceComponent());intent.addFlags(Intent.FLAG_DEBUG_TRIAGED_MISSING);//Slog.d(TAG, "Starting service: " + intent);context.startServiceAsUser(intent, UserHandle.SYSTEM);windowManager.onSystemUiStarted();}

//frameworks/base/services/core/java/com/android/server/pm/PackageManagerInternalBase.java@Override@Deprecatedpublic final ComponentName getSystemUiServiceComponent() {return ComponentName.unflattenFromString(getContext().getResources().getString(com.android.internal.R.string.config_systemUIServiceComponent));}

    <!-- SystemUi service component --><string name="config_systemUIServiceComponent" translatable="false">com.android.systemui/com.android.systemui.SystemUIService</string>

4.启动SystemUIService服务（SystemUI中）

public class SystemUIService extends Service {@Overridepublic void onCreate() {super.onCreate();// Start all of SystemUI((SystemUIApplication) getApplication()).startServicesIfNeeded();}
}

    启动实现了CoreStartable的实体类：如CentralSurfacesImpl等等，去start,去onBootCompleted/*** Makes sure that all the SystemUI services are running. If they are already running, this is a* no-op. This is needed to conditinally start all the services, as we only need to have it in* the main process.* <p>This method must only be called from the main thread.</p>*/public void startServicesIfNeeded() {final String vendorComponent = mInitializer.getVendorComponent(getResources());// Sort the startables so that we get a deterministic ordering.// TODO: make #start idempotent and require users of CoreStartable to call it.Map<Class<?>, Provider<CoreStartable>> sortedStartables = new TreeMap<>(Comparator.comparing(Class::getName));sortedStartables.putAll(mSysUIComponent.getStartables());sortedStartables.putAll(mSysUIComponent.getPerUserStartables());startServicesIfNeeded(sortedStartables, "StartServices", vendorComponent);}