Activity的ViewRoot的创建过程(二)

page4
    我们看一下ViewRootImpl对象的创建过程, ViewRootImpl类的声明如下:
    public final class ViewRootImpl implements ViewParent,
            View.AttachInfo.Callbacks, HardwareRenderer.HardwareDrawCallbacks

    ViewRootImpl类的构造函数定义如下:
    1     public ViewRootImpl(Context context, Display display) {
    2         super();
    3
    4         if (MEASURE_LATENCY) {
    5             if (lt == null) {
    6                 lt = new LatencyTimer(100, 1000);
    7             }
    8         }
    9
    10         // Initialize the statics when this class is first instantiated. This is
    11         // done here instead of in the static block because Zygote does not
    12         // allow the spawning of threads.
    13         mWindowSession = WindowManagerGlobal.getWindowSession(context.getMainLooper());
    14         mDisplay = display;
    15
    16         CompatibilityInfoHolder cih = display.getCompatibilityInfo();
    17         mCompatibilityInfo = cih != null ? cih : new CompatibilityInfoHolder();
    18
    19         mThread = Thread.currentThread();
    20         mLocation = new WindowLeaked(null);
    21         mLocation.fillInStackTrace();
    22         mWidth = -1;
    23         mHeight = -1;
    24         mDirty = new Rect();
    25         mTempRect = new Rect();
    26         mVisRect = new Rect();
    27         mWinFrame = new Rect();
    28         mWindow = new W(this);
    29         mTargetSdkVersion = context.getApplicationInfo().targetSdkVersion;
    30         mInputMethodCallback = new InputMethodCallback(this);
    31         mViewVisibility = View.GONE;
    32         mTransparentRegion = new Region();
    33         mPreviousTransparentRegion = new Region();
    34         mFirst = true; // true for the first time the view is added
    35         mAdded = false;
    36         mAccessibilityManager = AccessibilityManager.getInstance(context);
    37         mAccessibilityInteractionConnectionManager =
    38             new AccessibilityInteractionConnectionManager();
    39         mAccessibilityManager.addAccessibilityStateChangeListener(
    40                 mAccessibilityInteractionConnectionManager);
    41         mAttachInfo = new View.AttachInfo(mWindowSession, mWindow, display, this, mHandler, this);
    42         mViewConfiguration = ViewConfiguration.get(context);
    43         mDensity = context.getResources().getDisplayMetrics().densityDpi;
    44         mNoncompatDensity = context.getResources().getDisplayMetrics().noncompatDensityDpi;
    45         mFallbackEventHandler = PolicyManager.makeNewFallbackEventHandler(context);
    46         mProfileRendering = Boolean.parseBoolean(
    47                 SystemProperties.get(PROPERTY_PROFILE_RENDERING, "false"));
    48         mChoreographer = Choreographer.getInstance();
    49
    50         PowerManager powerManager = (PowerManager) context.getSystemService(Context.POWER_SERVICE);
    51         mAttachInfo.mScreenOn = powerManager.isScreenOn();
    52         loadSystemProperties();
    53     }

    第13行(ViewRootImpl->ViewRootImpl)会调用WindowManagerGlobal的getWindowSession函数, 关于getWindowSession函数的详细分析可以参考page5文件.

    第28行(ViewRootImpl->ViewRootImpl)会创建一个W类型的对象, 并用该对象来初始化成员变量mWindow. 关于W类型的构造过程可以参考page7文件.
    第41行(ViewRootImpl->ViewRootImpl)会创建一个AttachInfo对象, 表示ViewRootImpl所依附的Window的信息, 并用该AttachInfo对象初始化成员变量mAttachInfo.
page5
    我们分析一下WindowManagerGlobal的getWindowSession函数的实现:
    1     public static IWindowSession getWindowSession(Looper mainLooper) {
    2         synchronized (WindowManagerGlobal.class) {
    3             if (sWindowSession == null) {
    4                 try {
    5                     InputMethodManager imm = InputMethodManager.getInstance(mainLooper);
    6                     IWindowManager windowManager = getWindowManagerService();
    7                     sWindowSession = windowManager.openSession(
    8                             imm.getClient(), imm.getInputContext());
    9                     float animatorScale = windowManager.getAnimationScale(2);
    10                     ValueAnimator.setDurationScale(animatorScale);
    11                 } catch (RemoteException e) {
    12                     Log.e(TAG, "Failed to open window session", e);
    13                 }
    14             }
    15             return sWindowSession;
    16         }
    17     }
    第5行(WindowManagerGlobal->getWindowSession)
    第6行(WindowManagerGlobal->getWindowSession)会调用getWindowManagerService来得到WindowManager服务, 关于getWindowManagerService函数的详细分析可以参考page6文件.
    第7-8行(WindowManagerGlobal->getWindowSession)会用刚刚获得的WindowManagerService调用openSession函数,  其实这会导致和WindowManagerService建立连接. 关于和WindowManagerService建立连接的部分可以参考相关系列的文章.

    第15行(WindowManagerGlobal->getWindowSession)会返回和WindowManagerService的Session连接.
page6
WindowManagerGlobal的getWindowManagerService函数定义如下:
1     public static IWindowManager getWindowManagerService() {
2         synchronized (WindowManagerGlobal.class) {
3             if (sWindowManagerService == null) {
4                 sWindowManagerService = IWindowManager.Stub.asInterface(
5                         ServiceManager.getService("window"));
6             }
7             return sWindowManagerService;
8         }
9     }

WindowManagerGlobal的getWindowManagerService函数的主要逻辑就是通过Binder来获得"window"服务.