[深入SystemUI]-SystemUI_statusbar的启动流程

柔光的暖阳◎ 2022-01-20 09:29 207阅读 0赞

> 本文流程基于Android 9.0

# 1.启动SystemUIService #

在SystemServer中有一个方法startSystemUi，当系统启动后，会执行到SystemServer的startSystemUi()方法，正是在这个方法中启动了SystemUIService。

static final void startSystemUi(Context context, WindowManagerService windowManager) {
        Intent intent = new Intent();
        // 指定了systemui的包名"com.android.systemui"，指定了ServiceUIService的类名"com.android.systemui.SystemUIService"
        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);
        windowManager.onSystemUiStarted();
    }
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# 2.在SystemUIService中启动SystemUI中的服务 #

## SystemUIService.java ##

@Override
    public void onCreate() {
        super.onCreate();
        //在oncreate方法中调用SystemUIApplication的startServicesIfNeeded来启动相关服务
        ((SystemUIApplication) getApplication()).startServicesIfNeeded();
    
        // code...
    }
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## SystemUIApplication ##

/**
     * 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() {
        String[] names = getResources().getStringArray(R.array.config_systemUIServiceComponents);
        startServicesIfNeeded(names);
    }
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注意，这里的`service`的`names`是从`config`文件中读取出来的，具体内容如下，其中就包含了`SystemBars`的路径：

<string-array name="config_systemUIServiceComponents" translatable="false">
        <item>com.android.systemui.Dependency</item>
        <item>com.android.systemui.util.NotificationChannels</item>
        <item>com.android.systemui.statusbar.CommandQueue$CommandQueueStart</item>
        <item>com.android.systemui.keyguard.KeyguardViewMediator</item>
        <item>com.android.systemui.recents.Recents</item>
        <item>com.android.systemui.volume.VolumeUI</item>
        <item>com.android.systemui.stackdivider.Divider</item>
        <item>com.android.systemui.SystemBars</item>
        <item>com.android.systemui.usb.StorageNotification</item>
        <item>com.android.systemui.power.PowerUI</item>
        <item>com.android.systemui.media.RingtonePlayer</item>
        <item>com.android.systemui.keyboard.KeyboardUI</item>
        <item>com.android.systemui.pip.PipUI</item>
        <item>com.android.systemui.shortcut.ShortcutKeyDispatcher</item>
        <item>@string/config_systemUIVendorServiceComponent</item>
        <item>com.android.systemui.util.leak.GarbageMonitor$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.fingerprint.FingerprintDialogImpl</item>
        <item>com.android.systemui.SliceBroadcastRelayHandler</item>
    </string-array>
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具体的启动过程

private void startServicesIfNeeded(String[] services) {
        //这里就是方法名IfNeeded的原因，首先会判断boolean变量mServicesStarted是否为ture，为true，表示服务已经启动，就不需要执行后面的启动流程了
        if (mServicesStarted) {
            return;
        }
        //定义一个用于启动SystemUI服务的数组，并且这些要启动的服务都是继承自SystemUI的
        mServices = new SystemUI[services.length];
    
        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() + ".");
        TimingsTraceLog log = new TimingsTraceLog("SystemUIBootTiming",
                Trace.TRACE_TAG_APP);
        log.traceBegin("StartServices");
        final int N = services.length;
        //通过遍历，将所有的服务启动起来
        for (int i = 0; i < N; i++) {
            String clsName = services[i];
            if (DEBUG) Log.d(TAG, "loading: " + clsName);
            log.traceBegin("StartServices" + clsName);
            long ti = System.currentTimeMillis();
            Class cls;
            try {
                cls = Class.forName(clsName);
                mServices[i] = (SystemUI) cls.newInstance();
            } catch(ClassNotFoundException ex){
                throw new RuntimeException(ex);
            } catch (IllegalAccessException ex) {
                throw new RuntimeException(ex);
            } catch (InstantiationException ex) {
                throw new RuntimeException(ex);
            }
    
            mServices[i].mContext = this;
            mServices[i].mComponents = mComponents;
            if (DEBUG) Log.d(TAG, "running: " + mServices[i]);
            //调用各个服务重写了的start()方法
            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 " + cls.getName() + " took " + ti + " ms");
            }
            if (mBootCompleted) {
                mServices[i].onBootCompleted();
            }
        }
        // code...
    
        //启动过一次后，就将mServicesStarted置为true，避免重复启动
        mServicesStarted = true;
    }
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# 3.在SystemBars中启动statusbar #

关于`SystemBars`类的注释是这样的，“根据产品配置，使用进程内实现，确保一个`status bar`服务能够一直运行”。

/**
     * Ensure a single status bar service implementation is running at all times, using the in-process
     * implementation according to the product config.
     */
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那么status bar是怎样启动的呢？在SystemUIApplication中也是通过调用SystemBars的start()方法，在SystemBars中的start()方法中去启动statusbar。

@Override
    public void start() {
        if (DEBUG) Log.d(TAG, "start");
        createStatusBarFromConfig();
    }
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private void createStatusBarFromConfig() {
        if (DEBUG) Log.d(TAG, "createStatusBarFromConfig");
        final String clsName = mContext.getString(R.string.config_statusBarComponent);
        if (clsName == null || clsName.length() == 0) {
            throw andLog("No status bar component configured", null);
        }
        Class<?> cls = null;
        try {
            cls = mContext.getClassLoader().loadClass(clsName);
        } catch (Throwable t) {
            throw andLog("Error loading status bar component: " + clsName, t);
        }
        try {
            mStatusBar = (SystemUI) cls.newInstance();
        } catch (Throwable t) {
            throw andLog("Error creating status bar component: " + clsName, t);
        }
        mStatusBar.mContext = mContext;
        mStatusBar.mComponents = mComponents;
        mStatusBar.start();
        if (DEBUG) Log.d(TAG, "started " + mStatusBar.getClass().getSimpleName());
    }
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这里的clsName和之前服务的names一样，也是从config中读取的，具体如下，是StatusBar的类路径。

<string name="config_statusBarComponent" translatable="false">com.android.systemui.statusbar.phone.StatusBar</string>
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于是乎，通过这样一种方式，就启动起来一个一直运行着的StatusBar服务了。