关于ViewRootImpl

ViewRootImpl是view的最高层级，属于所有View的根，但它不是View，实现了viewParent接口，控件的测量、布局、绘制以及输入事件的派发处理都由ViewRootImpl触发，是view和windowManager的通信桥梁。

构造函数

老规矩，构造函数入手，看看初始化做了哪些事，在哪里初始化。

  public ViewRootImpl(Context context, Display display) {
        mContext = context;
        /*  从WindowManagerGlobal中获取一个IWindowSession的实例。它是ViewRootImpl和WMS进行通信的代理 */
        mWindowSession = WindowManagerGlobal.getWindowSession()；
        mDisplay = display;
        mBasePackageName = context.getBasePackageName();

        mDisplayAdjustments = display.getDisplayAdjustments();
        /*创建ViewRootImpl的线程为当前线程。再处理来自控件树的请求时，会检查
          发起请求的线程是否和当前线程相同，不同则会抛出异常*/
        mThread = Thread.currentThread();
        mLocation = new WindowLeaked(null);
        mLocation.fillInStackTrace();
        mWidth = -1;
        mHeight = -1;
        //收集窗口的无效区域
        mDirty = new Rect();
        mTempRect = new Rect();
        mVisRect = new Rect();
        //当前窗口的位置尺寸
        mWinFrame = new Rect();
        /*  创建一个W类型的实例，W是IWindow.Stub的子类。即它将在WMS中作为新         窗口的ID，以及接收来自WMS的回调*/
        mWindow = new W(this);
        mTargetSdkVersion = context.getApplicationInfo().targetSdkVersion;
        mViewVisibility = View.GONE;
        mTransparentRegion = new Region();
        mPreviousTransparentRegion = new Region();
        mFirst = true; // true for the first time the view is added
        mAdded = false;
        //创建View的内部类，AttachInfo实例，保存了多种信息，窗口实例，viewRootImpl实例等
        mAttachInfo = new View.AttachInfo(mWindowSession, mWindow, display, this, mHandler, this);
        mAccessibilityManager = AccessibilityManager.getInstance(context);
        mAccessibilityInteractionConnectionManager =
            new AccessibilityInteractionConnectionManager();
        mAccessibilityManager.addAccessibilityStateChangeListener(
                mAccessibilityInteractionConnectionManager);
        mHighContrastTextManager = new HighContrastTextManager();
        mAccessibilityManager.addHighTextContrastStateChangeListener(
                mHighContrastTextManager);
        mViewConfiguration = ViewConfiguration.get(context);
        mDensity = context.getResources().getDisplayMetrics().densityDpi;
        mNoncompatDensity = context.getResources().getDisplayMetrics().noncompatDensityDpi;
        mFallbackEventHandler = new PhoneFallbackEventHandler(context);
        mChoreographer = Choreographer.getInstance();
        mDisplayManager = (DisplayManager)context.getSystemService(Context.DISPLAY_SERVICE);
        loadSystemProperties();
    }

   

初始化

通过代码跟踪发现是在WindowManagerGlobal初始化，去看看里面跟viewRootImpl相关的代码

public final class WindowManagerGlobal {
    //所有window对象中的view
    private final ArrayList<View> mViews = new ArrayList<View>();
    //所有window对象中对应的viewRootImpl
    private final ArrayList<ViewRootImpl> mRoots = new ArrayList<ViewRootImpl>();
    //所有view对象的layoutParams
    private final ArrayList<WindowManager.LayoutParams> mParams =
            new ArrayList<WindowManager.LayoutParams>();
//···代码省略

 public void addView(View view, ViewGroup.LayoutParams params,
            Display display, Window parentWindow) {
    //代码省略```
           ViewRootImpl root;
           View panelParentView = null;

            if (wparams.type >= WindowManager.LayoutParams.FIRST_SUB_WINDOW &&
                    wparams.type <= WindowManager.LayoutParams.LAST_SUB_WINDOW) {
                final int count = mViews.size();
                for (int i = 0; i < count; i++) {
                    if (mRoots.get(i).mWindow.asBinder() == wparams.token) {
                        panelParentView = mViews.get(i);
                    }
                }
            }
          
           root = new ViewRootImpl(view.getContext(), display);

            view.setLayoutParams(wparams);
            //添加view
            mViews.add(view);
            //添加ViewRootImpl 
            mRoots.add(root);
            mParams.add(wparams);
             // do this last because it fires off messages to start doing things
        try {
            root.setView(view, wparams, panelParentView);
        }

}
}

不难看出，所有的view和viewRootImpl都同时加进同一个集合中，且有着顺序对应的关系。

在ViewRootImpl的构造函数中创建了以下几个主要对象：

(1) 通过WindowManagerGlobal.getWindowSession()得到IWindowSession的代理对象，该对象用于和WMS通信。

(2) 创建了一个W本地Binder对象mWindow，用于WMS通知应用程序进程。

(3) 创建ViewRootHandler对象，用于处理当前视图消息。

(4) 构造一个AttachInfo对象；

(5) 创建Surface对象，用于绘制当前视图，当然该Surface对象的真正创建是由WMS来完成的，只不过是WMS传递给应用程序进程的。

如何关联上

细心的朋友发现，在介绍WindowManagerGlobal 的addView()方法时，我没有去介绍ViewRootImpl的setView()方法。没错！就是通过这个方法，指定一个控件树管理，并向WMS添加一个新窗口后，ViewRootImpl的通信作用才显现出来。去看看setView里面做了啥事。

  public void setView(View view, WindowManager.LayoutParams attrs, View panelParentView) {
        synchronized (this) {
            if (mView == null) {
                //mView保存了控件的根
                mView = view;

                mAttachInfo.mDisplayState = mDisplay.getState();
                mDisplayManager.registerDisplayListener(mDisplayListener, mHandler);

                mViewLayoutDirectionInitial = mView.getRawLayoutDirection();
                mFallbackEventHandler.setView(view);
                //mWindowAttributes保存了窗口对应的LayoutParams
                mWindowAttributes.copyFrom(attrs);
                if (mWindowAttributes.packageName == null) {
                    mWindowAttributes.packageName = mBasePackageName;
                }
                attrs = mWindowAttributes;
                // Keep track of the actual window flags supplied by the client.
                mClientWindowLayoutFlags = attrs.flags;

                setAccessibilityFocus(null, null);

                if (view instanceof RootViewSurfaceTaker) {
                    mSurfaceHolderCallback =
                            ((RootViewSurfaceTaker)view).willYouTakeTheSurface();
                    if (mSurfaceHolderCallback != null) {
                        mSurfaceHolder = new TakenSurfaceHolder();
                        mSurfaceHolder.setFormat(PixelFormat.UNKNOWN);
                    }
                }

                // Compute surface insets required to draw at specified Z value.
                // TODO: Use real shadow insets for a constant max Z.
                if (!attrs.hasManualSurfaceInsets) {
                    final int surfaceInset = (int) Math.ceil(view.getZ() * 2);
                    attrs.surfaceInsets.set(surfaceInset, surfaceInset, surfaceInset, surfaceInset);
                }

                CompatibilityInfo compatibilityInfo = mDisplayAdjustments.getCompatibilityInfo();
                mTranslator = compatibilityInfo.getTranslator();

                // If the application owns the surface, don't enable hardware acceleration
                if (mSurfaceHolder == null) {
                    enableHardwareAcceleration(attrs);
                }

                boolean restore = false;
                if (mTranslator != null) {
                    mSurface.setCompatibilityTranslator(mTranslator);
                    restore = true;
                    attrs.backup();
                    mTranslator.translateWindowLayout(attrs);
                }
                if (DEBUG_LAYOUT) Log.d(TAG, "WindowLayout in setView:" + attrs);

                if (!compatibilityInfo.supportsScreen()) {
                    attrs.privateFlags |= WindowManager.LayoutParams.PRIVATE_FLAG_COMPATIBLE_WINDOW;
                    mLastInCompatMode = true;
                }

                mSoftInputMode = attrs.softInputMode;
                mWindowAttributesChanged = true;
                mWindowAttributesChangesFlag = WindowManager.LayoutParams.EVERYTHING_CHANGED;
                mAttachInfo.mRootView = view;
                mAttachInfo.mScalingRequired = mTranslator != null;
                mAttachInfo.mApplicationScale =
                        mTranslator == null ? 1.0f : mTranslator.applicationScale;
                if (panelParentView != null) {
                    mAttachInfo.mPanelParentWindowToken
                            = panelParentView.getApplicationWindowToken();
                }
                mAdded = true;
                int res; /* = WindowManagerImpl.ADD_OKAY; */

                /*在添加窗口之前，先通过requestLayout()方法遍历。最终是通过调用performTraversals()，这个方法实现了对控件树测量，布局，向WMS申请修改窗口属性以及重绘工作*/
                requestLayout();
                if ((mWindowAttributes.inputFeatures
                        & WindowManager.LayoutParams.INPUT_FEATURE_NO_INPUT_CHANNEL) == 0) {
                    mInputChannel = new InputChannel();
                }
                try {
                    mOrigWindowType = mWindowAttributes.type;
                    mAttachInfo.mRecomputeGlobalAttributes = true;
                    collectViewAttributes();
                    /*将窗口添加至到WMS中*/
                    res = mWindowSession.addToDisplay(mWindow, mSeq, mWindowAttributes,
                            getHostVisibility(), mDisplay.getDisplayId(),
                            mAttachInfo.mContentInsets, mAttachInfo.mStableInsets,
                            mAttachInfo.mOutsets, mInputChannel);
                } catch (RemoteException e) {
                    ···
                } finally {
                   ···
                }

                ···
                //错误处理，通常是权限问题，重复添加
                if (res < WindowManagerGlobal.ADD_OKAY) {
                    mAttachInfo.mRootView = null;
                    mAdded = false;
                    mFallbackEventHandler.setView(null);
                    unscheduleTraversals();
                    setAccessibilityFocus(null, null);
                    switch (res) {
                        case WindowManagerGlobal.ADD_BAD_APP_TOKEN:
                        case WindowManagerGlobal.ADD_BAD_SUBWINDOW_TOKEN:
                            throw new WindowManager.BadTokenException(
                                    "Unable to add window -- token " + attrs.token
                                    + " is not valid; is your activity running?");
                        case WindowManagerGlobal.ADD_NOT_APP_TOKEN:
                            throw new WindowManager.BadTokenException(
                                    "Unable to add window -- token " + attrs.token
                                    + " is not for an application");
                        case WindowManagerGlobal.ADD_APP_EXITING:
                            throw new WindowManager.BadTokenException(
                                    "Unable to add window -- app for token " + attrs.token
                                    + " is exiting");
                        case WindowManagerGlobal.ADD_DUPLICATE_ADD:
                            throw new WindowManager.BadTokenException(
                                    "Unable to add window -- window " + mWindow
                                    + " has already been added");
                        case WindowManagerGlobal.ADD_STARTING_NOT_NEEDED:
                            // Silently ignore -- we would have just removed it
                            // right away, anyway.
                            return;
                        case WindowManagerGlobal.ADD_MULTIPLE_SINGLETON:
                            throw new WindowManager.BadTokenException(
                                    "Unable to add window " + mWindow +
                                    " -- another window of this type already exists");
                        case WindowManagerGlobal.ADD_PERMISSION_DENIED:
                            throw new WindowManager.BadTokenException(
                                    "Unable to add window " + mWindow +
                                    " -- permission denied for this window type");
                        case WindowManagerGlobal.ADD_INVALID_DISPLAY:
                            throw new WindowManager.InvalidDisplayException(
                                    "Unable to add window " + mWindow +
                                    " -- the specified display can not be found");
                        case WindowManagerGlobal.ADD_INVALID_TYPE:
                            throw new WindowManager.InvalidDisplayException(
                                    "Unable to add window " + mWindow
                                    + " -- the specified window type is not valid");
                    }
                    throw new RuntimeException(
                            "Unable to add window -- unknown error code " + res);
                }

                if (view instanceof RootViewSurfaceTaker) {
                    mInputQueueCallback =
                        ((RootViewSurfaceTaker)view).willYouTakeTheInputQueue();
                }
                //如果mInputChannel ，则创建mInputEventReceiver 用于接收输入事件。
                创建时用的是主线程的Looper，即在主线程读取输入事件和触发事件，这是应用程序可以在ouTouchEvent()等事件响应UI操作的根本原因
                if (mInputChannel != null) {
                    if (mInputQueueCallback != null) {
                        mInputQueue = new InputQueue();
                        mInputQueueCallback.onInputQueueCreated(mInputQueue);
                    }
                    mInputEventReceiver = new WindowInputEventReceiver(mInputChannel,
                            Looper.myLooper());
                }
                 /* ViewRootImpl将作为参数view的parent。所以，ViewRootImpl可以从控件树中任何一个控件开始，通过回溯getParent()的方法得到 */
                view.assignParent(this);
           ···
            }
        }
    }

总结

至此，所有的成员变量已经初始完毕，新的窗口也添加进WMS中。ViewRootImpl的创建过程是由构造函数和setView()方法两个步骤完成的。其中构造函数主要进行成员的初始化，setView()则是创建窗口、建立输入事件接收机制的入口。