关于Android View体系里面的相关知识，可能会比较乱，先都罗列出来再说，后期再做整理。
自己做的笔记，不太适合学习用，大家看看就好，有问题烦请指正。
几个常用对象之间的关系
Activity 间接继承自 Context
activity.getWindow 获取到的是 PhoneWindow,继承自 Window(抽象类)
PhoneWIndow中持有mDecor① 和 mContentParent②：
①：mDecor = new DecorView()，间接继承ViewGroup DecorView extends FrameLayout extends ViewGroup
②：mContentParent = generateLayout(mDecor);
protected ViewGroup generateLayout(DecorView decor)
mContentParent是ViewGroup对象
setContentView的执行
-
getWindow().setContentView(resID),其中window对象在Activity的attach()方法中初始化 （PhoneWindow） -
PhoneWindow.setCOntentView()源码如下：@Override public void setContentView(int layoutResID) { // Note: FEATURE_CONTENT_TRANSITIONS may be set in the process of installing the window // decor, when theme attributes and the like are crystalized. Do not check the feature // before this happens. //阳氏翻译：在insatllDecor()过程中可能会设置FEATURE_CONTENT_TRANSITIONS的值，直到theme属性明确 if (mContentParent == null) { installDecor();//这里面new了mDecor和mContentParent俩对象 } else if (!hasFeature(FEATURE_CONTENT_TRANSITIONS)) { mContentParent.removeAllViews(); } if (hasFeature(FEATURE_CONTENT_TRANSITIONS)) { final Scene newScene = Scene.getSceneForLayout(mContentParent, layoutResID, getContext()); transitionTo(newScene); } else { mLayoutInflater.inflate(layoutResID, mContentParent);//布局加载到mContentParent中去 } mContentParent.requestApplyInsets(); final Callback cb = getCallback(); if (cb != null && !isDestroyed()) { cb.onContentChanged(); } mContentParentExplicitlySet = true; }关注后两个注释即可，一个初始化了
Decor和ContentParent;一个加载了布局。installDecor()中有这两句：①：mDecor = generateDecor(); ②：
mContentParent = generateLayout(mDecor);大致如图：
activity构成.png
事件分发机制
白话
依上图可见，手指触摸屏幕瞬间会触发Activity.dispatchTouchEvent,依次传递到window、decor直到ViewGroup.dispatchTouchEvent()方法中来。
跟着，ViewGroup的dispatchTouchEvent方法中一堆逻辑判断，判断是否拦截。
如果拦截，跳转到ViewGroup.onTouchEvent();
如果不拦截，则遍历child，执行child.dispatchTouchEvent()方法；
child是view的话，在 view.dispatchTouchEvent()方法中先判断有无 touchListener,
有的话执行touchLIstener，否则 执行 view.onTouchEvent()方法
代码可抽象成这样：
//不是源码！！！！！
public boolean dispatchTouchEvent(MotionEvent ev){
boolean result = false;
//这里就是判断是否拦截的一堆逻辑
if(onInterceptTouchEvent(ev)){
result = super.onTouchEvent(ev);
}else{
result = child.dispatchTouchEvent(ev)
}
return result;
}
后续： view.onTouchEvent()中，若view的clickable或LongClickable为true 且 ＡＣＴＩＯＮ＿ＵＰ ，则调用 performClick()方法;
performClick()方法中对onCLickListener 进行了响应：mListenerInfo.mOnClickListener.onClick(this)
图示
事件分发流程
对了，默认情况下ViewGroup.onInterceptTouchEvent()返回false，即默认可以一条路走下来。
View的工作流程
当我们调用Activity的startActivity()方法时，最终是调用ActivityThread.handleLaunchActivity方法 来创建Activity的。
public Activity handleLaunchActivity(ActivityClientRecord r, Intent customIntent) {
...
// Initialize before creating the activity
WindowManagerGlobal.initialize();
/** performLaunchActivity: Core implementation(核心实现) of activity launch. */
//这里书上说会调用到onCreate()方法中来，我看源码中调用到了attach()方法
Activity a = performLaunchActivity(r, customIntent);
if (a != null) {
r.createdConfig = new Configuration(mConfiguration);
Bundle oldState = r.state;
//handleResumeActivity 代码在下面
handleResumeActivity(r.token, false, r.isForward,
!r.activity.mFinished && !r.startsNotResumed);
...
}
final void handleResumeActivity(IBinder token, boolean clearHide, boolean isForward, boolean reallyResume) {
//Resume the activity.
ActivityClientRecord r = performResumeActivity(token, clearHide);
if (r != null) {
final Activity a = r.activity;
...
if (r.window == null && !a.mFinished && willBeVisible) {
r.window = r.activity.getWindow();//getWindow
View decor = r.window.getDecorView();//getDecooView
decor.setVisibility(View.INVISIBLE);
ViewManager wm = a.getWindowManager();//getWindowManager
WindowManager.LayoutParams l = r.window.getAttributes();
a.mDecor = decor;
l.type = WindowManager.LayoutParams.TYPE_BASE_APPLICATION;
l.softInputMode |= forwardBit;
if (a.mVisibleFromClient) {
a.mWindowAdded = true;
//WindowManager是接口，实际调用的WindowManagerImpl.addView()
//不管怎么说，这里至少已经把decor传到了windowmanager中去了
//不过界面上看不出来，必须要等measure、layout、draw 三板斧走完才能看到
wm.addView(decor, l);
}
...
}
...
}
}
可以看出handleResumeActivity中最终是把布局委托给了WindowManager去创建。
WindowManager是一个接口，主要实现是在WindowManagerImpl中：
@Override
public void addView(@NonNull View view, @NonNull ViewGroup.LayoutParams params) {
applyDefaultToken(params);
mGlobal.addView(view, params, mContext.getDisplayNoVerify(), mParentWindow,
mContext.getUserId());
}
跟着又用到了mGlobal.addView()方法，mGlobal是windowManagerGlobal对象，windowManagerGlobal中addView方法如下：
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) {
...
// If this is a panel window, then find the window it is being
// attached to for future reference.
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);
}
}
}
//①初始化ViewRootImpl
root = new ViewRootImpl(view.getContext(), display);
view.setLayoutParams(wparams);
mViews.add(view);
mRoots.add(root);
mParams.add(wparams);
// do this last because it fires off messages to start doing things
try {
//②穿进去的view ，即是上文中的Decor
//至此，Decor就传入到了window中去了
root.setView(view, wparams, panelParentView, userId);
} catch (RuntimeException e) {
// BadTokenException or InvalidDisplayException, clean up.
if (index >= 0) {
removeViewLocked(index, true);
}
throw e;
}
}
}
②中的root即ViewRootImpl,ViewRootImpl还有一个方法 PerformTraversals()。这个方法使得ViewTree开始View的工作流程。performMeasure、performLayout、performDraw方法都在里面。对应measure、layout、draw方法。
提一句，里面的performMeasure()会传入两个参数 performMeasure(childWidthMeasureSpec, childHeightMeasureSpec);
MeasureSpec的最顶层
PerformTraversals中，有如下代码：
if(!mStopped){
int childWidthMeasureSpec = getRootMeasureSpec(mWidth, lp.width);
int childHeightMeasureSpec = getRootMeasureSpec(mHeight, lp.height);
// Ask host how big it wants to be
performMeasure(childWidthMeasureSpec, childHeightMeasureSpec);
}
MeasureSpec是一个32位的int值，前两位表示mode,后30位代表size。这个应该要展开来讲，不清楚的可以网上看看。
这里的performMeasure中传入的两个值就是最顶层的MeasureSpec。由 getRootMeasureSpec()方法获取：
private static int getRootMeasureSpec(int windowSize, int rootDimension) {
int measureSpec;
switch (rootDimension) {
case ViewGroup.LayoutParams.MATCH_PARENT:
// Window can't resize. Force root view to be windowSize.
measureSpec = MeasureSpec.makeMeasureSpec(windowSize, MeasureSpec.EXACTLY);
break;
case ViewGroup.LayoutParams.WRAP_CONTENT:
// Window can resize. Set max size for root view.
measureSpec = MeasureSpec.makeMeasureSpec(windowSize, MeasureSpec.AT_MOST);
break;
default:
// Window wants to be an exact size. Force root view to be that size.
measureSpec = MeasureSpec.makeMeasureSpec(rootDimension, MeasureSpec.EXACTLY);
break;
}
return measureSpec;
}
windowSize是窗口的尺寸，（19201080或者是2660*1440等，根据设备而定）；
然后根据LayoutParams具体是什么来设置measureSpec。代码写的很清楚。
再往下走，看performMeasure()方法：
private void performMeasure(int childWidthMeasureSpec, int childHeightMeasureSpec) {
if (mView == null) {
return;
}
Trace.traceBegin(Trace.TRACE_TAG_VIEW, "measure");
try {
//************熟悉的measure方法啊*************
mView.measure(childWidthMeasureSpec, childHeightMeasureSpec);
} finally {
Trace.traceEnd(Trace.TRACE_TAG_VIEW);
}
}
关键就那一句，熟悉的measure方法开始了。
不要忘了mView是谁，没错，就是上文（ViewRootImpl.setView()）中传来的view，上上文(windowManager.addView())中传来的view——mDecor。
如果你记忆力还比较好的话，你应该记得文章开头的地方列出了decor的继承关系——继承自ViewGroup。
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