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。
