一. DecorView的创建
1. 创建Window抽象类的子类PhoneWindow类的实例对象
2.为PhoneWindow类对象设置WindowManager对象
3.为PhoneWindow类对象创建DecorView类对象（根据所选主题样式）
4. 为DecorView类对象中的content增加Activity中设置的布局文件
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@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
}
public void setContentView(int layoutResID) {
getWindow().setContentView(layoutResID);
initWindowDecorActionBar();
}
mWindow = new PhoneWindow(this, window);
mWindow.setWindowControllerCallback(this);
mWindow.setCallback(this);
mWindow.setWindowManager(
(WindowManager)context.getSystemService(Context.WINDOW_SERVICE),
mToken, mComponent.flattenToString(),
(info.flags & ActivityInfo.FLAG_HARDWARE_ACCELERATED) != 0);
}
public void setContentView(int layoutResID) {
if (mContentParent == null) {
installDecor();
} else {
mContentParent.removeAllViews();
}
mLayoutInflater.inflate(layoutResID, mContentParent);
final Callback cb = getCallback();
if (cb != null && !isDestroyed()) {
cb.onContentChanged();
}
}
private void installDecor() {
if (mDecor == null) {
mDecor = generateDecor();
mDecor.setDescendantFocusability(ViewGroup.FOCUS_AFTER_DESCENDANTS);
mDecor.setIsRootNamespace(true);
if (!mInvalidatePanelMenuPosted && mInvalidatePanelMenuFeatures != 0) {
mDecor.postOnAnimation(mInvalidatePanelMenuRunnable);
}
}
if (mContentParent == null) {
mContentParent = generateLayout(mDecor);
...
}
}
protected DecorView generateDecor() {
return new DecorView(getContext(), -1);
}
protected ViewGroup generateLayout(DecorView decor) {
TypedArray a = getWindowStyle();
int layoutResource;
int features = getLocalFeatures();
View in = mLayoutInflater.inflate(layoutResource, null);
decor.addView(in, new ViewGroup.LayoutParams(MATCH_PARENT, MATCH_PARENT));
mContentRoot = (ViewGroup) in;
ViewGroup contentParent = (ViewGroup)findViewById(ID_ANDROID_CONTENT);
return contentParent;
}
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此时，顶层View（DecorView）已创建 并且 添加Activity中设置的布局文件。但是，此时，顶层View（DecorView）仍未显示出来，即不可见。
二. DecorView的显示
在主线程创建时，会调用 handleResumeActivity()，这里有DecorView的显示的流程：
1.将DecorView对象添加到WindowManager中。
2.创建ViewRootImpl对象。
3.WindowManager将DecorView对象交给ViewRootImpl对象。
4.ViewRootImpl对象通过Handler向主线程发送一条触发遍历操作的消息：performTraversals()，该方法用于执行View的绘制流程(measure，layout，draw)。
ViewRootImpl对象中接受的各种变化，如来自WindowManagerService的窗口属性变化，来自控件树的尺寸变化或者重绘请求等都会引发performTraversals()的调用并且在其中完成处理。
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@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
}
final void handleResumeActivity(IBinder token,
boolean clearHide, boolean isForward, boolean reallyResume) {
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();
View decor = r.window.getDecorView();
decor.setVisibility(View.INVISIBLE);
ViewManager wm = a.getWindowManager();
WindowManager.LayoutParams l = r.window.getAttributes();
a.mDecor = decor;
l.type = WindowManager.LayoutParams.TYPE_BASE_APPLICATION;
if (a.mVisibleFromClient) {
a.mWindowAdded = true;
wm.addView(decor, l);
}
if (!r.activity.mFinished && willBeVisible
&& r.activity.mDecor != null && !r.hideForNow) {
if (r.activity.mVisibleFromClient) {
r.activity.makeVisible();
}
}
}
void makeVisible() {
if (!mWindowAdded) {
ViewManager wm = getWindowManager();
wm.addView(mDecor, getWindow().getAttributes());
mWindowAdded = true;
}
mDecor.setVisibility(View.VISIBLE);
}
public final class WindowManagerImpl implements WindowManager {
private final WindowManagerGlobal mGlobal = WindowManagerGlobal.getInstance();
...
@Override
public void addView(View view, ViewGroup.LayoutParams params) {
mGlobal.addView(view, params, mDisplay, mParentWindow); ->>分析3
}
}
public void addView(View view, ViewGroup.LayoutParams params,Display display, Window parentWindow) {
final WindowManager.LayoutParams wparams = (WindowManager.LayoutParams)params;
...
synchronized (mLock) {
ViewRootImpl root;
root = new ViewRootImpl(view.getContext(), display);
view.setLayoutParams(wparams);
mViews.add(view);
mRoots.add(root);
mParams.add(wparams);
}
try {
root.setView(view, wparams, panelParentView);
}catch (RuntimeException e) {
...
}
}
public void setView(View view, WindowManager.LayoutParams attrs, View panelParentView) {
requestLayout();
}
@Override
public void requestLayout() {
if (!mHandlingLayoutInLayoutRequest) {
checkThread();
mLayoutRequested = true;
scheduleTraversals();
}
}
void scheduleTraversals() {
if (!mTraversalScheduled) {
mTraversalScheduled = true;
mTraversalBarrier = mHandler.getLooper().getQueue().postSyncBarrier();
mChoreographer.postCallback(Choreographer.CALLBACK_TRAVERSAL, mTraversalRunnable, null);
``````
}
}
final class TraversalRunnable implements Runnable {
@Override
public void run() {
doTraversal();
}
}
final TraversalRunnable mTraversalRunnable = new TraversalRunnable();
void doTraversal() {
mHandler.getLooper().getQueue().removeSyncBarrier(mTraversalBarrier);
performTraversals();
}
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