前面介绍了ViewRootImpl与Choreographer的相互配合刷新界面：界面是如何刷新的流程
ViewRootImpl的描述是这样的：
The top of a view hierarchy, implementing the needed protocol between View and the WindowManager. This is for the most part an internal implementation detail of WindowManagerGlobal
翻译一下
View层次结构的顶部，实现视图和窗口管理器之间所需的协议。这在很大程度上是一种WindowManagerGlobal详细的内部实现
View mView作为ViewRootImpl的一个属性，承担了所有和视图相关的操作。
我们可以猜测 mView就是用户看到的屏幕界面。
为了验证猜测，下面我们看一下mView是从哪里来的，是怎么添加到ViewRootImpl中的。
绑定视图到Window
从最熟悉的地方开始：
#Activity
public void setContentView(View view, ViewGroup.LayoutParams params) {
getWindow().setContentView(view, params);
}
Window的实现类是PhoneWindow，Decor是Activity View视图最外层的ViewGroup，由PhoneWindow创建：
#PhoneWindow
@Override
public void setContentView(View view, ViewGroup.LayoutParams params) {
installDecor();
mContentParent.addView(view, params);
}
Window和WindowManager的创建
在Activity的attach创建了PhoneWindow的实例：
#Activity
final void attach() {
mWindow = new PhoneWindow(this, window, activityConfigCallback);
mWindow.setWindowManager(
(WindowManager)context.getSystemService(Context.WINDOW_SERVICE),
mToken, mComponent.flattenToString(),
(info.flags & ActivityInfo.FLAG_HARDWARE_ACCELERATED) != 0);
}
PhoneWindow的父类Window设置WindowManager
#Window
public void setWindowManager(WindowManager wm, IBinder appToken, String appName,
boolean hardwareAccelerated) {
if (wm == null) {
wm = (WindowManager)mContext.getSystemService(Context.WINDOW_SERVICE);
}
mWindowManager = ((WindowManagerImpl)wm).createLocalWindowManager(this);
}
现在我们知道Activity创建了一个Window：PhoneWindow，PhoneWindow中有ViewGroup：Decor，还有WindowManager
绑定View和WindowManager
handleResumeActivity方法中，调用了WindowManager的add方法，第一个参数是decor，这个WindowManager就是上文说PhoneWindow的WindowManager：
#ActivityThread
@Override
public void handleResumeActivity(IBinder token, boolean finalStateRequest, boolean isForward,
String reason) {
final ActivityClientRecord r = performResumeActivity(token, finalStateRequest, reason);
final Activity a = r.activity;
if (r.window == null && !a.mFinished && willBeVisible) {
r.window = r.activity.getWindow();
//Decor
View decor = r.window.getDecorView();
decor.setVisibility(View.INVISIBLE);
//WindowManager
ViewManager wm = a.getWindowManager();
WindowManager.LayoutParams l = r.window.getAttributes();
a.mDecor = decor;
if (a.mVisibleFromClient) {
if (!a.mWindowAdded) {
a.mWindowAdded = true;
//Add
wm.addView(decor, l);
} else {
a.onWindowAttributesChanged(l);
}
}
}
}
添加view到Global
WindowManagerImpl是WindowManager的实现类：
#WindowManagerImpl
private final WindowManagerGlobal mGlobal = WindowManagerGlobal.getInstance();
@Override
public void addView(@NonNull View view, @NonNull ViewGroup.LayoutParams params) {
applyDefaultToken(params);
mGlobal.addView(view, params, mContext.getDisplayNoVerify(), mParentWindow,
mContext.getUserId());
}
绑定WindowManagerGlobal和ViewRootImpl
WindowManagerGlobal.addView创建了ViewRootImpl，并且设置了View
#WindowManagerGlobal
public void addView(View view, ViewGroup.LayoutParams params,
Display display, Window parentWindow, int userId) {
final WindowManager.LayoutParams wparams = (WindowManager.LayoutParams) params;
ViewRootImpl root;
View panelParentView = null;
synchronized (mLock) {
root = new ViewRootImpl(view.getContext(), display);
view.setLayoutParams(wparams);
mViews.add(view);
mRoots.add(root);
mParams.add(wparams);
root.setView(view, wparams, panelParentView, userId);
}
}
总结
- Activity创建PhoneWindow
- Activity设置PhoneWindow的View和WindowManager
- Activity Resume时，通过WindowManager添加View
- WindowManager实际调用的WindowManagerGlobal
- WindowManagerGlobal创建了ViewRootImpl，并且给ViewRootImpl设置View