android12 SystemUI启动流程

开机，init->init.rc->zygote->启动system_server进程. SystemServer->run()->startOtherService()->ActivityManagerService.systemReady()->startSystemUI();

public static void main(String[] args) {
    new SystemServer().run();
}

// Start services.
try {
    t.traceBegin("StartServices");
    startBootstrapServices(t);
    startCoreServices(t);
    startOtherServices(t);
} catch (Throwable ex) {
    Slog.e("System", "******************************************");
    Slog.e("System", "************ Failure starting system services", ex);
    throw ex;
} finally {
    t.traceEnd(); // StartServices
}

mActivityManagerService.systemReady(() -> {
t.traceBegin("StartSystemUI");
try {
    startSystemUi(context, windowManagerF);
} catch (Throwable e) {
    reportWtf("starting System UI", e);
}
t.traceEnd();
}, t);

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

---PackageManagerService.PackageManagerInternalImpl
@Override
public ComponentName getSystemUiServiceComponent() {
    return ComponentName.unflattenFromString(mContext.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>

启动SystemUIService->SystemUIService.onCreate->SystemUIApplication.startServicesIfNeeded()->读取配置config_systemUIServiceComponents中的组件，依次调用这些组件的start()来启动状态栏，导航栏等组件 。

@Override
public void onCreate() {
    super.onCreate();

    // Start all of SystemUI
    ((SystemUIApplication) getApplication()).startServicesIfNeeded();
    
}

public void startServicesIfNeeded() {
    String[] names = SystemUIFactory.getInstance().getSystemUIServiceComponents(getResources());
    startServicesIfNeeded(/* metricsPrefix= */ "StartServices", names);
}

public String[] getSystemUIServiceComponents(Resources resources) {
    return resources.getStringArray(R.array.config_systemUIServiceComponents);
    
}

<string-array name="config_systemUIServiceComponents" translatable="false">
315         <item>com.android.systemui.util.NotificationChannels</item>
316         <item>com.android.systemui.keyguard.KeyguardViewMediator</item>
317         <item>com.android.systemui.recents.Recents</item>
318         <item>com.android.systemui.volume.VolumeUI</item>
319         <item>com.android.systemui.statusbar.phone.StatusBar</item>
320         <item>com.android.systemui.usb.StorageNotification</item>
321         <item>com.android.systemui.power.PowerUI</item>
322         <item>com.android.systemui.media.RingtonePlayer</item>
323         <item>com.android.systemui.keyboard.KeyboardUI</item>
324         <item>com.android.systemui.shortcut.ShortcutKeyDispatcher</item>
325         <item>@string/config_systemUIVendorServiceComponent</item>
326        <item>com.android.systemui.util.leak.GarbageMonitor$Service</item>
327         <item>com.android.systemui.LatencyTester</item>
328    <item>com.android.systemui.globalactions.GlobalActionsComponent</item>
329         <item>com.android.systemui.ScreenDecorations</item>
330         <item>com.android.systemui.biometrics.AuthController</item>
331         <item>com.android.systemui.SliceBroadcastRelayHandler</item>
332<item>com.android.systemui.statusbar.notification.InstantAppNotifier</item>
333<item>com.android.systemui.theme.ThemeOverlayController</item>
334       <item>com.android.systemui.accessibility.WindowMagnification</item>
335         <item>com.android.systemui.accessibility.SystemActions</item>
336         <item>com.android.systemui.toast.ToastUI</item>
337         <item>com.android.systemui.wmshell.WMShell</item>
338     </string-array>