android SystemUI浅析之SystemUI启动流程

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我是靠谱客的博主缥缈歌曲，这篇文章主要介绍android SystemUI浅析之SystemUI启动流程，现在分享给大家，希望可以做个参考。

前言：最近在研究4.2的status bar 和navigation bar，想做一下总结，后来碰到一篇文章分享一下，至于4.2上的变化以及4.2上的总结，我会在后期补充上并且会一直修改和完善。参考http://blog.csdn.net/yihongyuelan

我们知道Android 4.0以后SystemUI同时适用于Phone和Tablet(TV)，因此，对于Phone来说SystemUI指的是：StatusBar(状态栏)、NavigationBar(导航栏)。而对于Tablet或者是TV来说SystemUI指的是：CombinedBar(包括了StatusBar和NavigationBar)。

首先来看看SystemUI的代码位置，路径：SourceCode/frameworks/base/packages/SystemUI。

那么接下来怎么分析呢？打开AndroidManifest.xml可以看到：

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<manifest xmlns:android="http://schemas.android.com/apk/res/android"  
        package="com.android.systemui"  
        coreApp="true"  
        android:sharedUserId="android.uid.system"  
        android:process="system"  
        >  
  
    <uses-permission android:name="android.permission.STATUS_BAR_SERVICE" />  
    <uses-permission android:name="android.permission.BLUETOOTH" />  
    <uses-permission android:name="android.permission.BLUETOOTH_ADMIN" />  
    <uses-permission android:name="android.permission.GET_TASKS" />  
    <uses-permission android:name="android.permission.MANAGE_USB" />  
  
    <application  
        android:persistent="true"  
        android:allowClearUserData="false"  
        android:allowBackup="false"  
        android:hardwareAccelerated="true"  
        android:label="@string/app_label"  
        android:icon="@drawable/ic_launcher_settings">  
  
        <!-- Broadcast receiver that gets the broadcast at boot time and starts  
             up everything else.  
             TODO: Should have an android:permission attribute  
             -->  
        <service android:name="SystemUIService"  
            android:exported="true"  
            />  
  
        <!-- started from PhoneWindowManager  
             TODO: Should have an android:permission attribute -->  
        <service android:name=".screenshot.TakeScreenshotService"  
            android:process=":screenshot"  
            android:exported="false" />  
  
        <service android:name=".LoadAverageService"  
                android:exported="true" />  
  
        <service android:name=".ImageWallpaper"  
                android:permission="android.permission.BIND_WALLPAPER"  
                android:exported="true" />  
  
        <receiver android:name=".BootReceiver" >  
            <intent-filter>  
                <action android:name="android.intent.action.BOOT_COMPLETED" />  
            </intent-filter>  
        </receiver>  
        ... ...  
    </application>  
</manifest>

根据以上代码我们可以发现这其中注册了很多Service，同时也包括了广播。但这里我们只关注SystemUIService，这才是本文的主旨啊。那么首先要找到SystemUIService是如何启动的。对于Service的启动，在我以前的博文中已有提到，这里就不多说了，不外乎startService(intent)和bindService(intent)，它们都是以intent为对象，那intent的声明也需要SystemUIService啊，因此我们可以据此搜索关键词"SystemUIService"。

最终发现SystemUIService是在SystemServer.java中被启动的，如下所示：

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static final void startSystemUi(Context context) {  
    Intent intent = new Intent();  
    intent.setComponent(new ComponentName("com.android.systemui",  
                "com.android.systemui.SystemUIService"));  
    Slog.d(TAG, "Starting service: " + intent);  
    context.startService(intent);  
}

这里的startSystemUi()方法则在ServerThread的run()方法中被调用。这里提到SystemServer就不得不提及Android的启动流程，这里不会展开详细讨论具体的流程，只是简单的介绍一下大概流程，用以表明SystemServer所处的位置。

Android的启动分为内核启动、Android启动、launcher启动，我们的SystemServer就处于Android启动中，以下是大致流程图：

init->ServiceManager->Zygote->SystemServer->... ...

在SystemServer中，初始化了Android系统中的Java层服务，如PowerManagerService、WindowManagerService等等，当然也包括了SystemUIService，它们通过ServiceManager的addService()方法，添加到ServiceManager的管理中。实际上，根据后面的分析这里add了一个很重要的StatusBarManagerService。这个Service在后面会用到的。

既然到这里SystemUIService已经启动，那么我们就继续跟踪该Service吧。

1).首先查看其onCreate()方法，如下：

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public void onCreate() {  
    // Pick status bar or system bar.   
    IWindowManager wm = IWindowManager.Stub.asInterface(  
            ServiceManager.getService(Context.WINDOW_SERVICE));  
    try {  
        SERVICES[0] = wm.canStatusBarHide()//根据wm.canStatusBarHide()判断设备类型   
                ? R.string.config_statusBarComponent  
                : R.string.config_systemBarComponent;  
    } catch (RemoteException e) {  
        Slog.w(TAG, "Failing checking whether status bar can hide", e);  
    }  
  
    final int N = SERVICES.length;  
    mServices = new SystemUI[N];  
    for (int i=0; i<N; i++) {  
        Class cl = chooseClass(SERVICES[i]);  
        Slog.d(TAG, "loading: " + cl);  
        try {  
            mServices[i] = (SystemUI)cl.newInstance();  
        } catch (IllegalAccessException ex) {  
            throw new RuntimeException(ex);  
        } catch (InstantiationException ex) {  
            throw new RuntimeException(ex);  
        }  
        mServices[i].mContext = this;  
        Slog.d(TAG, "running: " + mServices[i]);  
        mServices[i].start();  
    }  
}

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public void onCreate() {  
    // Pick status bar or system bar.   
    IWindowManager wm = IWindowManager.Stub.asInterface(  
            ServiceManager.getService(Context.WINDOW_SERVICE));  
    try {  
        SERVICES[0] = wm.canStatusBarHide()//根据wm.canStatusBarHide()判断设备类型   
                ? R.string.config_statusBarComponent  
                : R.string.config_systemBarComponent;  
    } catch (RemoteException e) {  
        Slog.w(TAG, "Failing checking whether status bar can hide", e);  
    }  
  
    final int N = SERVICES.length;  
    mServices = new SystemUI[N];  
    for (int i=0; i<N; i++) {  
        Class cl = chooseClass(SERVICES[i]);  
        Slog.d(TAG, "loading: " + cl);  
        try {  
            mServices[i] = (SystemUI)cl.newInstance();  
        } catch (IllegalAccessException ex) {  
            throw new RuntimeException(ex);  
        } catch (InstantiationException ex) {  
            throw new RuntimeException(ex);  
        }  
        mServices[i].mContext = this;  
        Slog.d(TAG, "running: " + mServices[i]);  
        mServices[i].start();  
    }  
}

在这段代码中，通过AIDL的方式获取了WindowManager的对象wm，并调用其方法canStatusBarHide()来判断当前设备的类型，也就是说如果我们使用的Phone那么后续就会加载StatusBar和NivagationBar；而如果我们设备类型是Tablet(TV)之类的(可以在配置文档里面配置)，就会加载CombiedBar。

这里的canStatusBarHide()方法的具体实现是在：frameworks/base/policy/src/com/android/internal/policy/impl/PhoneWindowManager.java。为什么会是这里呢？我们在Eclipse中导入源码之后，找到SystemUIService.java中的wm.canStatusBarHide()方法，通过open Implementation直接跳转到WindowsManagerService中：

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public boolean canStatusBarHide() {  
    return mPolicy.canStatusBarHide();  
}

但这里我们发现canStatusBarHide()实际上是WindowManagerPolicy的对象调用的方法，而WindowManagerPolicy只是一个接口类，根据以往分析的经验可以知道，这里的WindowManagerPolicy对象所调用的canStatusBartHide()方法一定是其实现类中的方法。因此，继续通过open Implementation跳转，来到了PhoneWindownManager中：

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public boolean canStatusBarHide() {  
    return mStatusBarCanHide;  
}

继续查看mSatuBarCanHide的实现，如下所示：

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// Determine whether the status bar can hide based on the size   
// of the screen.  We assume sizes > 600dp are tablets where we   
// will use the system bar.   
int shortSizeDp = shortSize  
        * DisplayMetrics.DENSITY_DEFAULT  
        / DisplayMetrics.DENSITY_DEVICE;  
mStatusBarCanHide = shortSizeDp < 600;  
mStatusBarHeight = mContext.getResources().getDimensionPixelSize(  
        mStatusBarCanHide  
        ? com.android.internal.R.dimen.status_bar_height  
        : com.android.internal.R.dimen.system_bar_height);  
  
mHasNavigationBar = mContext.getResources().getBoolean(  
        com.android.internal.R.bool.config_showNavigationBar);

这里通过shortSizeDp来判断当前设备的类型，如果当前屏幕的shortSizeDp<600dp，则系统会认为该设备是Phone反之则认为是Tablet。根据mStatusBarCanHide的值，设定StatusBar或者SystemBar(CombinedBar)的高度，以及是否显示NavigationBar。

继续回到我们的SystemUIService.java的onCreate()方法中，根据前面对canStatusBarHide()的判断，SERVICE[0]中将存放R.string.config_statusBarComponent或者R.string.config_systemBarComponent。它们的值具体是：

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<string name="config_statusBarComponent" translatable="false">com.android.systemui.statusbar.phone.PhoneStatusBar</string>  
<string name="config_systemBarComponent" translatable="false">com.android.systemui.statusbar.tablet.TabletStatusBar</string>

因为我的测试设备是Phone，那么现在SERVICE[0]中存放的就是com.android.systemui.statusbart.phone.PhoneStatusBar。查看以下代码：

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final int N = SERVICES.length;  
mServices = new SystemUI[N];  
for (int i=0; i<N; i++) {  
    Class cl = chooseClass(SERVICES[i]);  
    Slog.d(TAG, "loading: " + cl);  
    try {  
        mServices[i] = (SystemUI)cl.newInstance();  
    } catch (IllegalAccessException ex) {  
        throw new RuntimeException(ex);  
    } catch (InstantiationException ex) {  
        throw new RuntimeException(ex);  
    }  
    mServices[i].mContext = this;  
    Slog.d(TAG, "running: " + mServices[i]);  
    mServices[i].start();  
}

这些方法会分别启动两个方法，这两个方法可以从log中知道，分别是PhoneStatusBar.start()和PowerUI.start()。而我们的目的是要弄清SystemUI的启动，因此现关注PhoneStatusBar.start()方法。

log信息：

06-04 13:23:15.379: DEBUG/SystemUIService(396): loading: class com.android.systemui.statusbar.phone.PhoneStatusBar

06-04 13:23:16.739: DEBUG/SystemUIService(396): loading: class com.android.systemui.power.PowerUI

来到PhoneStatusBar.start()方法中，位于：SourceCode/frameworks/base/packages/SystemUI/src/com/android/systemui/statusbar/phone/PhoneStatusBar.java，代码如下：

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@Override  
public void start() {  
    mDisplay = ((WindowManager)mContext.getSystemService(Context.WINDOW_SERVICE))  
            .getDefaultDisplay();  
  
    mWindowManager = IWindowManager.Stub.asInterface(  
            ServiceManager.getService(Context.WINDOW_SERVICE));  
  
    super.start(); // calls makeStatusBarView()   
  
    addNavigationBar();  
  
    //addIntruderView();   
  
    // Lastly, call to the icon policy to install/update all the icons.   
    mIconPolicy = new PhoneStatusBarPolicy(mContext);  
}

这里的重心主要是在super.start()和addNavigationBar()上。目前市面上很多手机已经刷入了ICS，但是大多数是没有NavigationBar的，也就是说自己修改了源码，屏蔽了NavigationBar。继续跟踪super.start()方法，来到/SourceCode/frameworks/base/packages/SystemUI/src/com/android/systemui/statusbar/StatusBar.java的start()方法中，代码如下：

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public void start() {  
    // First set up our views and stuff.   
    View sb = makeStatusBarView();  
  
    // Connect in to the status bar manager service   
    StatusBarIconList iconList = new StatusBarIconList();  
    ArrayList<IBinder> notificationKeys = new ArrayList<IBinder>();  
    ArrayList<StatusBarNotification> notifications = new ArrayList<StatusBarNotification>();  
    mCommandQueue = new CommandQueue(this, iconList);  
    mBarService = IStatusBarService.Stub.asInterface(  
            ServiceManager.getService(Context.STATUS_BAR_SERVICE));  
    int[] switches = new int[7];  
    ArrayList<IBinder> binders = new ArrayList<IBinder>();  
    try {  
        mBarService.registerStatusBar(mCommandQueue, iconList, notificationKeys, notifications,  
                switches, binders);  
    } catch (RemoteException ex) {  
        // If the system process isn't there we're doomed anyway.   
    }  
  
    disable(switches[0]);  
    setSystemUiVisibility(switches[1]);  
    topAppWindowChanged(switches[2] != 0);  
    // StatusBarManagerService has a back up of IME token and it's restored here.   
    setImeWindowStatus(binders.get(0), switches[3], switches[4]);  
    setHardKeyboardStatus(switches[5] != 0, switches[6] != 0);  
  
    // Set up the initial icon state   
    int N = iconList.size();  
    int viewIndex = 0;  
    for (int i=0; i<N; i++) {  
        StatusBarIcon icon = iconList.getIcon(i);  
        if (icon != null) {  
            addIcon(iconList.getSlot(i), i, viewIndex, icon);  
            viewIndex++;  
        }  
    }  
  
    // Set up the initial notification state   
    N = notificationKeys.size();  
    if (N == notifications.size()) {  
        for (int i=0; i<N; i++) {  
            addNotification(notificationKeys.get(i), notifications.get(i));  
        }  
    } else {  
        Log.wtf(TAG, "Notification list length mismatch: keys=" + N  
                + " notifications=" + notifications.size());  
    }  
  
    // Put up the view   
    final int height = getStatusBarHeight();  
  
    final WindowManager.LayoutParams lp = new WindowManager.LayoutParams(  
            ViewGroup.LayoutParams.MATCH_PARENT,  
            height,  
            WindowManager.LayoutParams.TYPE_STATUS_BAR,  
            WindowManager.LayoutParams.FLAG_NOT_FOCUSABLE  
                | WindowManager.LayoutParams.FLAG_TOUCHABLE_WHEN_WAKING  
                | WindowManager.LayoutParams.FLAG_SPLIT_TOUCH,  
            // We use a pixel format of RGB565 for the status bar to save memory bandwidth and   
            // to ensure that the layer can be handled by HWComposer.  On some devices the   
            // HWComposer is unable to handle SW-rendered RGBX_8888 layers.   
            PixelFormat.RGB_565);  
      
    // the status bar should be in an overlay if possible   
    final Display defaultDisplay   
        = ((WindowManager)mContext.getSystemService(Context.WINDOW_SERVICE))  
            .getDefaultDisplay();  
  
    // We explicitly leave FLAG_HARDWARE_ACCELERATED out of the flags.  The status bar occupies   
    // very little screen real-estate and is updated fairly frequently.  By using CPU rendering   
    // for the status bar, we prevent the GPU from having to wake up just to do these small   
    // updates, which should help keep power consumption down.   
  
    lp.gravity = getStatusBarGravity();  
    lp.setTitle("StatusBar");  
    lp.packageName = mContext.getPackageName();  
    lp.windowAnimations = R.style.Animation_StatusBar;  
    WindowManagerImpl.getDefault().addView(sb, lp);  
  
    if (SPEW) {  
        Slog.d(TAG, "Added status bar view: gravity=0x" + Integer.toHexString(lp.gravity)   
               + " icons=" + iconList.size()  
               + " disabled=0x" + Integer.toHexString(switches[0])  
               + " lights=" + switches[1]  
               + " menu=" + switches[2]  
               + " imeButton=" + switches[3]  
               );  
    }  
  
    mDoNotDisturb = new DoNotDisturb(mContext);  
}

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public void start() {  
    // First set up our views and stuff.   
    View sb = makeStatusBarView();  
  
    // Connect in to the status bar manager service   
    StatusBarIconList iconList = new StatusBarIconList();  
    ArrayList<IBinder> notificationKeys = new ArrayList<IBinder>();  
    ArrayList<StatusBarNotification> notifications = new ArrayList<StatusBarNotification>();  
    mCommandQueue = new CommandQueue(this, iconList);  
    mBarService = IStatusBarService.Stub.asInterface(  
            ServiceManager.getService(Context.STATUS_BAR_SERVICE));  
    int[] switches = new int[7];  
    ArrayList<IBinder> binders = new ArrayList<IBinder>();  
    try {  
        mBarService.registerStatusBar(mCommandQueue, iconList, notificationKeys, notifications,  
                switches, binders);  
    } catch (RemoteException ex) {  
        // If the system process isn't there we're doomed anyway.   
    }  
  
    disable(switches[0]);  
    setSystemUiVisibility(switches[1]);  
    topAppWindowChanged(switches[2] != 0);  
    // StatusBarManagerService has a back up of IME token and it's restored here.   
    setImeWindowStatus(binders.get(0), switches[3], switches[4]);  
    setHardKeyboardStatus(switches[5] != 0, switches[6] != 0);  
  
    // Set up the initial icon state   
    int N = iconList.size();  
    int viewIndex = 0;  
    for (int i=0; i<N; i++) {  
        StatusBarIcon icon = iconList.getIcon(i);  
        if (icon != null) {  
            addIcon(iconList.getSlot(i), i, viewIndex, icon);  
            viewIndex++;  
        }  
    }  
  
    // Set up the initial notification state   
    N = notificationKeys.size();  
    if (N == notifications.size()) {  
        for (int i=0; i<N; i++) {  
            addNotification(notificationKeys.get(i), notifications.get(i));  
        }  
    } else {  
        Log.wtf(TAG, "Notification list length mismatch: keys=" + N  
                + " notifications=" + notifications.size());  
    }  
  
    // Put up the view   
    final int height = getStatusBarHeight();  
  
    final WindowManager.LayoutParams lp = new WindowManager.LayoutParams(  
            ViewGroup.LayoutParams.MATCH_PARENT,  
            height,  
            WindowManager.LayoutParams.TYPE_STATUS_BAR,  
            WindowManager.LayoutParams.FLAG_NOT_FOCUSABLE  
                | WindowManager.LayoutParams.FLAG_TOUCHABLE_WHEN_WAKING  
                | WindowManager.LayoutParams.FLAG_SPLIT_TOUCH,  
            // We use a pixel format of RGB565 for the status bar to save memory bandwidth and   
            // to ensure that the layer can be handled by HWComposer.  On some devices the   
            // HWComposer is unable to handle SW-rendered RGBX_8888 layers.   
            PixelFormat.RGB_565);  
      
    // the status bar should be in an overlay if possible   
    final Display defaultDisplay   
        = ((WindowManager)mContext.getSystemService(Context.WINDOW_SERVICE))  
            .getDefaultDisplay();  
  
    // We explicitly leave FLAG_HARDWARE_ACCELERATED out of the flags.  The status bar occupies   
    // very little screen real-estate and is updated fairly frequently.  By using CPU rendering   
    // for the status bar, we prevent the GPU from having to wake up just to do these small   
    // updates, which should help keep power consumption down.   
  
    lp.gravity = getStatusBarGravity();  
    lp.setTitle("StatusBar");  
    lp.packageName = mContext.getPackageName();  
    lp.windowAnimations = R.style.Animation_StatusBar;  
    WindowManagerImpl.getDefault().addView(sb, lp);  
  
    if (SPEW) {  
        Slog.d(TAG, "Added status bar view: gravity=0x" + Integer.toHexString(lp.gravity)   
               + " icons=" + iconList.size()  
               + " disabled=0x" + Integer.toHexString(switches[0])  
               + " lights=" + switches[1]  
               + " menu=" + switches[2]  
               + " imeButton=" + switches[3]  
               );  
    }  
  
    mDoNotDisturb = new DoNotDisturb(mContext);  
}

在这里，完成了SystemUI的整个初始化以及设置过程，并最终呈现到界面上。在StatusBar中的start()方法主要完成了以下几个工作：首先获取需要在StatusBar上显示的各种icons。然后初始化一些属性。最后通过WindowManager的addView方法将StatusBar显示出来。分析到这里可能有人会问了，明明说分析的是SystemUI的嘛，怎么最后变成StatusBar了呢？如果你硬要说我跑题那我也没有办法，回过头去看看addNavigationBar()，你会发现和StatusBar的加载几乎一致，因此没必要再详述了。如果细心阅读了的朋友肯定会发现这句代码：

mBarService = IStatusBarService.Stub.asInterface(ServiceManager.getService(Context.STATUS_BAR_SERVICE));

这不正是我们前面add的StatusBarManagerSerivce吗？这里通过AIDL的方式来获取它的对象。

整个代码执行的时序图如图2.2所示：

图2.2

3.总结

Android 4.0的SystemUI加载启动的过程大致就是这样，虽然看似简单，但这仅仅是个开始，master还是后面呢！！各家厂商根据自家的需求，需要定制SystemUI或者美化SystemUI，不同的平台(QCOM、MTK等等)也会有不同的修改，但大体框架是没有变的，无非是在原有基础上的修修改改或者增加一些自己的类等等。通过对Android源码框架性的理解，可以学习到很多设计上的知识（虽然自己还很欠缺）。通过这次分析，开始逐渐用StarUML来画时序图，这也是一个学习的过程。