什么是SystemUI

SystemUI是一个系统级apk，位于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。

private void startOtherServices(@NonNull TimingsTraceAndSlog t) {
    mActivityManagerService.systemReady(() -> {
            Slog.i(TAG, "Making services ready");
            t.traceBegin("StartActivityManagerReadyPhase");
            mSystemServiceManager.startBootPhase(t, SystemService.PHASE_ACTIVITY_MANAGER_READY);
            t.traceEnd();
            t.traceBegin("StartObservingNativeCrashes");
            try {
                mActivityManagerService.startObservingNativeCrashes();
            } catch (Throwable e) {
                reportWtf("observing native crashes", e);
            }
            t.traceEnd();
 
            // No dependency on Webview preparation in system server. But this should
            // be completed before allowing 3rd party
            final String WEBVIEW_PREPARATION = "WebViewFactoryPreparation";
            Future<?> webviewPrep = null;
            if (!mOnlyCore && mWebViewUpdateService != null) {
                webviewPrep = SystemServerInitThreadPool.submit(() -> {
                    Slog.i(TAG, WEBVIEW_PREPARATION);
                    TimingsTraceAndSlog traceLog = TimingsTraceAndSlog.newAsyncLog();
                    traceLog.traceBegin(WEBVIEW_PREPARATION);
                    ConcurrentUtils.waitForFutureNoInterrupt(mZygotePreload, "Zygote preload");
                    mZygotePreload = null;
                    mWebViewUpdateService.prepareWebViewInSystemServer();
                    traceLog.traceEnd();
                }, WEBVIEW_PREPARATION);
            }
 
            if (mPackageManager.hasSystemFeature(PackageManager.FEATURE_AUTOMOTIVE)) {
                t.traceBegin("StartCarServiceHelperService");
                mSystemServiceManager.startService(CAR_SERVICE_HELPER_SERVICE_CLASS);
                t.traceEnd();
            }
 
            t.traceBegin("StartSystemUI");
            try {
                startSystemUi(context, windowManagerF);
            } catch (Throwable e) {
                reportWtf("starting System UI", e);
            }
 
}

    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\android\content\pm\PackageManagerInternal.java

   /**
     * @return The SystemUI service component name.
     */
    public abstract ComponentName getSystemUiServiceComponent();

抽象方法，具体实现在  PackageManagerService

mContext 是系统的

frameworks/base/services/core/java/com/android/server/pm/PackageManagerService.java实现

@Override
            public ComponentName getSystemUiServiceComponent() {
            return ComponentName.unflattenFromString(mContext.getResources().getString(
                    com.android.internal.R.string.config_systemUIServiceComponent));
        }

frameworks\base\core\res\res\values\config.xml

    
    <string name="config_systemUIServiceComponent" translatable="false"
            >com.android.systemui/com.android.systemui.SystemUIServicestring>

启动SystemUIService

frameworks\base\packages\SystemUI\src\com\android\systemui\SystemUIService.java

调用startServicesIfNeeded启动一系列服务

    public void onCreate() {
        super.onCreate();
 
        // Start all of SystemUI
        ((SystemUIApplication) getApplication()).startServicesIfNeeded();
 
        // Finish initializing dump logic
        mLogBufferFreezer.attach(mBroadcastDispatcher);
 
        // For debugging RescueParty
        if (Build.IS_DEBUGGABLE && SystemProperties.getBoolean("debug.crash_sysui", false)) {
            throw new RuntimeException();
        }
 
        if (Build.IS_DEBUGGABLE) {
            // b/71353150 - looking for leaked binder proxies
            BinderInternal.nSetBinderProxyCountEnabled(true);
            BinderInternal.nSetBinderProxyCountWatermarks(1000,900);
            BinderInternal.setBinderProxyCountCallback(
                    new BinderInternal.BinderProxyLimitListener() {
                        @Override
                        public void onLimitReached(int uid) {
                            Slog.w(SystemUIApplication.TAG,
                                    "uid " + uid + " sent too many Binder proxies to uid "
                                    + Process.myUid());
                        }
                    }, mMainHandler);
        }
 
        // Bind the dump service so we can dump extra info during a bug report
        startServiceAsUser(
                new Intent(getApplicationContext(), SystemUIAuxiliaryDumpService.class),
                UserHandle.SYSTEM);
    }

frameworks\base\packages\SystemUI\src\com\android\systemui\SystemUIApplication.java 

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

调用 mServices[i].start();启动service

    private void startServicesIfNeeded(String metricsPrefix, String[] services) {
        if (mServicesStarted) {
            return;
        }
        mServices = new SystemUI[services.length];
 
        if (!mBootCompleteCache.isBootComplete()) {
            // check to see if maybe it was already completed long before we began
            // see ActivityManagerService.finishBooting()
            if ("1".equals(SystemProperties.get("sys.boot_completed"))) {
                mBootCompleteCache.setBootComplete();
                if (DEBUG) {
                    Log.v(TAG, "BOOT_COMPLETED was already sent");
                }
            }
        }
 
        final DumpManager dumpManager = mRootComponent.createDumpManager();
 
        Log.v(TAG, "Starting SystemUI services for user " +
                Process.myUserHandle().getIdentifier() + ".");
        TimingsTraceLog log = new TimingsTraceLog("SystemUIBootTiming",
                Trace.TRACE_TAG_APP);
        log.traceBegin(metricsPrefix);
        final int N = services.length;
        for (int i = 0; i < N; i++) {
            String clsName = services[i];
            if (DEBUG) Log.d(TAG, "loading: " + clsName);
            log.traceBegin(metricsPrefix + clsName);
            long ti = System.currentTimeMillis();
            try {
                SystemUI obj = mComponentHelper.resolveSystemUI(clsName);
                if (obj == null) {
                    Constructor constructor = Class.forName(clsName).getConstructor(Context.class);
                    obj = (SystemUI) constructor.newInstance(this);
                }
                mServices[i] = obj;
            } catch (ClassNotFoundException
                    | NoSuchMethodException
                    | IllegalAccessException
                    | InstantiationException
                    | InvocationTargetException ex) {
                throw new RuntimeException(ex);
            }
 
            if (DEBUG) Log.d(TAG, "running: " + mServices[i]);
            mServices[i].start();
            log.traceEnd();
 
            // Warn if initialization of component takes too long
            ti = System.currentTimeMillis() - ti;
            if (ti > 1000) {
                Log.w(TAG, "Initialization of " + clsName + " took " + ti + " ms");
            }
            if (mBootCompleteCache.isBootComplete()) {
                mServices[i].onBootCompleted();
            }
 
            dumpManager.registerDumpable(mServices[i].getClass().getName(), mServices[i]);
        }
        mRootComponent.getInitController().executePostInitTasks();
        log.traceEnd();
 
        mServicesStarted = true;
    }

 

mContext 是SystemUI

frameworks\base\packages\SystemUI\src\com\android\systemui\SystemUIFactory.java

    /** Returns the list of system UI components that should be started. */
    public String[] getSystemUIServiceComponents(Resources resources) {
        return resources.getStringArray(R.array.config_systemUIServiceComponents);
    }

frameworks\base\packages\SystemUI\res\values\config.xml

    <!-- SystemUI Services: The classes of the stuff to start. -->
    <string-array name="config_systemUIServiceComponents" translatable="false">
        <item>com.android.systemui.util.NotificationChannels</item>
        <item>com.android.systemui.keyguard.KeyguardViewMediator</item>
        <item>com.android.systemui.recents.Recents</item>
        <item>com.android.systemui.volume.VolumeUI</item>
        <item>com.android.systemui.stackdivider.Divider</item>
        <item>com.android.systemui.statusbar.phone.StatusBar</item>
        <item>com.android.systemui.usb.StorageNotification</item>
        <item>com.android.systemui.power.PowerUI</item>
        <item>com.android.systemui.media.RingtonePlayer</item>
        <item>com.android.systemui.keyboard.KeyboardUI</item>
        <item>com.android.systemui.pip.PipUI</item>
        <item>com.android.systemui.shortcut.ShortcutKeyDispatcher</item>
        <item>@string/config_systemUIVendorServiceComponent</item>
        <item>com.android.systemui.util.leak.GarbageMonitor$Service</item>
        <item>com.android.systemui.LatencyTester</item>
        <item>com.android.systemui.globalactions.GlobalActionsComponent</item>
        <item>com.android.systemui.ScreenDecorations</item>
        <item>com.android.systemui.biometrics.AuthController</item>
        <item>com.android.systemui.SliceBroadcastRelayHandler</item>
        <item>com.android.systemui.SizeCompatModeActivityController</item>
        <item>com.android.systemui.statusbar.notification.InstantAppNotifier</item>
        <item>com.android.systemui.theme.ThemeOverlayController</item>
        <item>com.android.systemui.accessibility.WindowMagnification</item>
        <item>com.android.systemui.accessibility.SystemActions</item>
        <item>com.android.systemui.toast.ToastUI</item>
    </string-array>

所有UI均继承自systemUI

frameworks\base\packages\SystemUI\src\com\android\systemui\SystemUI.java

public class PowerUI extends SystemUI implements CommandQueue.Callbacks {