Android 7.0 SystemUI(1)--启动过程

最新推荐文章于 2025-07-03 09:26:07 发布

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最新推荐文章于 2025-07-03 09:26:07 发布 · 2.2k 阅读

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本文详细探讨了Android 7.0中SystemUI的启动过程，从SystemServer.java的main()方法开始，通过context的startServiceAsUser启动SystemUIService。讲解了在system_server进程中如何进行，并简略了Binder通信，直接关注ActivityManagerService的startService方法。

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本文基于Android 7.0，记录SystemUI学习过程，如有错误之处请谅解。

涉及到的代码

frameworks/base/services/java/com/android/server/SystemServer.java
frameworks/base/core/java/android/app/ContextImpl.java
frameworks/base/services/core/java/com/android/server/am/ActiveServices.java 
frameworks/base/services/core/java/com/android/server/am/ActivityManagerService.java 
frameworks/base/core/java/android/app/ActivityThread.java
frameworks/base/packages/SystemUI/

SystemUI是系统app，源码位于framework/base/package/SystemUI。

SystemUI启动是从frameworks/base/services/java/com/android/server/SystemServer.java main()开始的。

 /**
     * The main entry point from zygote.
     */
    public static void main(String[] args) {
        new SystemServer().run();
    }

进入到run()中

private void run() {
        
	...

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

       ...
	   
    }

所有的系统服务都是在这里启动的，其中在startBootstrapServices()中启动了ActivityManagerService、PowerManagerService、PackageManagerService等一系列核心服务，SystemUI是在startOtherServices()中。

/**
     * Starts a miscellaneous grab bag of stuff that has yet to be refactored
     * and organized.
     */
    private void startOtherServices(){

		...

        WindowManagerService wm = null;

       
		...
     
        try {
           
         ...
          
            wm = WindowManagerService.main(context, inputManager,
                    mFactoryTestMode != FactoryTest.FACTORY_TEST_LOW_LEVEL,
                    !mFirstBoot, mOnlyCore);
            ServiceManager.addService(Context.WINDOW_SERVICE, wm);
            ...
        } catch (RuntimeException e) {
            Slog.e("System", "******************************************");
            Slog.e("System", "************ Failure starting core service", e);
        }

		...
		
        StatusBarManagerService statusBar = null;
        INotificationManager notification = null;
       
	   ...

        if (mFactoryTestMode != FactoryTest.FACTORY_TEST_LOW_LEVEL) {
           ...

            if (!disableSystemUI) {
                traceBeginAndSlog("StartStatusBarManagerService");
                try {
                    statusBar = new StatusBarManagerService(context, wm);
                    ServiceManager.addService(Context.STATUS_BAR_SERVICE, statusBar);
                } catch (Throwable e) {
                    reportWtf("starting StatusBarManagerService", e);
                }
                Trace.traceEnd(Trace.TRACE_TAG_SYSTEM_SERVER);
            }

           ...
		   
            mSystemServiceManager.startService(NotificationManagerService.class);
            notification = INotificationManager.Stub.asInterface(
                    ServiceManager.getService(Context.NOTIFICATION_SERVICE));
           ...
          
        }
		...
        // We now tell the activity manager it is okay to run third party
        // code.  It will call back into us once it has gotten to the state
        // where third party code can really run (but before it has actually
        // started launching the initial applications), for us to complete our
        // initialization.
        mActivityManagerService.systemReady(new Runnable() {
            @Override
            public void run() {
                ...

                Trace.traceBegin(Trace.TRACE_TAG_SYSTEM_SERVER, "StartSystemUI");
                try {
                    startSystemUi(context);
                } catch (Throwable e) {
                    reportWtf("starting System UI", e);
                }
				
                ...
            }
        });
       
    }

startOtherServices()还启动了大名鼎鼎的WindowManagerService。然后启动StatusBarManagerService，该服务是用来和SystemUI交互的。所有的系统服务启动完成之后，ams会调用systemReady去真正开始启动SystemUI。

frameworks/base/services/java/com/android/server/SystemServer.java

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);
    }

可以看到这里是通过context的startServiceAsUser去启动SystemUIService。该方法的真正实现是在ContextImpl.java

frameworks/base/core/java/android/app/ContextImpl.java

    @Override
    public ComponentName startServiceAsUser(Intent service, UserHandle user) {
        return startServiceCommon(service, user);
    }

    private ComponentName startServiceCommon(Intent service, UserHandle user) {
        try {
            validateServiceIntent(service);
            service.prepareToLeaveProcess(this);
            ComponentName cn = ActivityManagerNative.getDefault().startService(
                mMainThread.getApplicationThread(), service, service.resolveTypeIfNeeded(
                            getContentResolver()), getOpPackageName(), user.getIdentifier());
            if (cn != null) {
                if (cn.getPackageName().equals("!")) {
                    throw new SecurityEx