本文基于Android 9.0
1. 前言
前面一篇文章简要的概括了一下WindowManager的架构，WindowManager归根到底还是对Window的操作，本文同样暂时不涉及WMS，具体详细的讲一讲Window的添加与更新操作，为后面剖析WMS打下扎实的基础。
2. Window
2.1 Winow的类型
Window的类型有很多种，在WindowMangaer中定义了很多的Type。其实细细的整理一下，Window的类型其实分为三大类，Application Window、Sub Window、 System Window，这三大类里面根据不同场景又分了很多子类供外部使用，详细的Type描述，可以在WindowManager的静态内部类LayoutParams中查看。接下来根据三种不同类型的Window，一一举例讲一下他们的添加流程。
2.2 Window的添加流程
2.2.1 Application Window的添加流程
Application Window最典型的就是Activity，下面就来讲一下Activity的Window部分操作的流程。在Activity启动过程中，如果Activity所在的进程不存在，那么系统就会创建一个新的进程，这个时候就会创建代表该应用主线程的实例ActivityThread，在Activity的启动过程中，会调用ActivityThread的handleResumeActivity方法，其代码如下：
@Override
public void handleResumeActivity(IBinder token, boolean finalStateRequest, boolean isForward,
String reason) {
...
// TODO Push resumeArgs into the activity for consideration
final ActivityClientRecord r = performResumeActivity(token, finalStateRequest, reason);
...
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;
l.softInputMode |= forwardBit;
if (r.mPreserveWindow) {
a.mWindowAdded = true;
r.mPreserveWindow = false;
// Normally the ViewRoot sets up callbacks with the Activity
// in addView->ViewRootImpl#setView. If we are instead reusing
// the decor view we have to notify the view root that the
// callbacks may have changed.
ViewRootImpl impl = decor.getViewRootImpl();
if (impl != null) {
impl.notifyChildRebuilt();
}
}
if (a.mVisibleFromClient) {
if (!a.mWindowAdded) {
a.mWindowAdded = true;
wm.addView(decor, l);
} else {
// The activity will get a callback for this {@link LayoutParams} change
// earlier. However, at that time the decor will not be set (this is set
// in this method), so no action will be taken. This call ensures the
// callback occurs with the decor set.
a.onWindowAttributesChanged(l);
}
}
...
}
该方法中performResumeActivity就会触发Activity的onResume方法。这里可以看到通过ViewManager获取到wm对象，并把decor调用ViewManager的addView添加窗口。前面文章讲过，addView真正实现是在WindowManagerImpl中，其具体代码如下：
@Override
public void addView(@NonNull View view, @NonNull ViewGroup.LayoutParams params) {
applyDefaultToken(params);
mGlobal.addView(view, params, mContext.getDisplay(), mParentWindow);
}
上一篇中讲到，其实addView也没有在WindowManagerImpl实现，而是继续委托给了WindowManagerGlobal来实现，这里来看一下WindowManagerGlobal中addView的逻辑：
public void addView(View view, ViewGroup.LayoutParams params,
Display display, Window parentWindow) {
...
final WindowManager.LayoutParams wparams = (WindowManager.LayoutParams) params;
if (parentWindow != null) {
parentWindow.adjustLayoutParamsForSubWindow(wparams);
} else {
// If there's no parent, then hardware acceleration for this view is
// set from the application's hardware acceleration setting.
final Context context = view.getContext();
if (context != null
&& (context.getApplicationInfo().flags
& ApplicationInfo.FLAG_HARDWARE_ACCELERATED) != 0) {
wparams.flags |= WindowManager.LayoutParams.FLAG_HARDWARE_ACCELERATED;
}
}
ViewRootImpl root;
View panelParentView = null;
synchronized (mLock) {
// Start watching for system property changes.
if (mSystemPropertyUpdater == null) {
mSystemPropertyUpdater = new Runnable() {
@Override public void run() {
synchronized (mLock) {
for (int i = mRoots.size() - 1; i >= 0; --i) {
mRoots.get(i).loadSystemProperties();
}
}
}
};
SystemProperties.addChangeCallback(mSystemPropertyUpdater);
}
int index = findViewLocked(view, false);
if (index >= 0) {
if (mDyingViews.contains(view)) {
// Don't wait for MSG_DIE to make it's way through root's queue.
mRoots.get(index).doDie();
} else {
throw new IllegalStateException("View " + view
+ " has already been added to the window manager.");
}
// The previous removeView() had not completed executing. Now it has.
}
// 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);
}
}
}
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 {
root.setView(view, wparams, panelParentView);
} catch (RuntimeException e) {
// BadTokenException or InvalidDisplayException, clean up.
if (index >= 0) {
removeViewLocked(index, true);
}
throw e;
}
}
}
这里细心的同学可以发现三个列表，mViews、mRoots以及mParams，他们分别是View列表、ViewRootImpl列表和布局参数Params列表。这里比较特殊的就是ViewRootImpl，从代码中看，最后root调用setView来继续执行流程。这个ViewRootImpl到底是何方神圣呢？该类具有以下特点：
- View树的根节点管理View树
- 负责与WMS进程间通讯
- 触发View的onMeasure、onLayout以及onDraw
- 管理Surface
- Input事件的中转
上面说道最后调用了ViewRootImpl的setView方法，其代码逻辑如下：
/**
* We have one child
*/
public void setView(View view, WindowManager.LayoutParams attrs, View panelParentView) {
synchronized (this) {
...
try {
mOrigWindowType = mWindowAttributes.type;
mAttachInfo.mRecomputeGlobalAttributes = true;
collectViewAttributes();
res = mWindowSession.addToDisplay(mWindow, mSeq, mWindowAttributes,
getHostVisibility(), mDisplay.getDisplayId(), mWinFrame,
mAttachInfo.mContentInsets, mAttachInfo.mStableInsets,
mAttachInfo.mOutsets, mAttachInfo.mDisplayCutout, mInputChannel);
}
...
}
}
}
此函数逻辑很长，这里截取我们需要的部分进行讲解，这里就是调用了mWindowSession的addToDisplay方法，mWindowSession是一个binder对象，IWindowSession是一个Client端代理，Session端是在WMS中，所以Session的addToDisplay是运行在WMS中，这里可以看一下Session中addToDisplay的逻辑：
@Override
public int addToDisplay(IWindow window, int seq, WindowManager.LayoutParams attrs,
int viewVisibility, int displayId, Rect outFrame, Rect outContentInsets,
Rect outStableInsets, Rect outOutsets,
DisplayCutout.ParcelableWrapper outDisplayCutout, InputChannel outInputChannel) {
return mService.addWindow(this, window, seq, attrs, viewVisibility, displayId, outFrame,
outContentInsets, outStableInsets, outOutsets, outDisplayCutout, outInputChannel);
}
在Session中addToDisplay方法中调用了WMS的addWindow方法，剩下的工作就全部交给WMS处理，这里先不细致讲解，大概的工作流程就是交给WMS后，WMS会给待添加的window分配surface，并确定window的显示次序，最后交给SurfaceFlinger处理，SurfaceFlinger会将这些Surface混合并绘制到屏幕上。这里将整个流程的时序图梳理一下：
2.2.2 Sub Window的添加流程
前面已经梳理了Application Window的流程，接下来快速梳理一下Sub Window的流程，Sub Window最典型的代表就是PopupWindow，众所周知，PopupWindow的display方法是showAsDropDown，这里来看一下showAsDropDown的具体逻辑：
public void showAsDropDown(View anchor, int xoff, int yoff, int gravity) {
if (isShowing() || !hasContentView()) {
return;
}
TransitionManager.endTransitions(mDecorView);
attachToAnchor(anchor, xoff, yoff, gravity);
mIsShowing = true;
mIsDropdown = true;
final WindowManager.LayoutParams p =
createPopupLayoutParams(anchor.getApplicationWindowToken());
preparePopup(p);
final boolean aboveAnchor = findDropDownPosition(anchor, p, xoff, yoff,
p.width, p.height, gravity, mAllowScrollingAnchorParent);
updateAboveAnchor(aboveAnchor);
p.accessibilityIdOfAnchor = (anchor != null) ? anchor.getAccessibilityViewId() : -1;
invokePopup(p);
}
可以看到，首先通过createPopupLayoutParams来创建窗口属性，然后交给invokePopup来创建，创建逻辑如下：
private void invokePopup(WindowManager.LayoutParams p) {
if (mContext != null) {
p.packageName = mContext.getPackageName();
}
final PopupDecorView decorView = mDecorView;
decorView.setFitsSystemWindows(mLayoutInsetDecor);
setLayoutDirectionFromAnchor();
mWindowManager.addView(decorView, p);
if (mEnterTransition != null) {
decorView.requestEnterTransition(mEnterTransition);
}
}
这里又看到熟悉的身影，调用的WindowManager的addView，接下来流程就和前面Application Window添加的流程大体一致了，这里也不再去重复描述了。
2.2.3 System Window的添加流程
System Window流程，这里我们选取一个常见的System Window——NavigationBar来讲一下，NavigationBar是SystemUI的重要组成部分，主要功能是用来存放Home键、Back键以及最近任务键，并响应对应的操作。Navigationbar的创建在SystemUI的Statusbar类中，当SystemUI初始化的时候会调用makeStatusBarView方法，该方法中会进行创建Navigationbar的操作，具体逻辑如下：
protected void makeStatusBarView() {
...
try {
boolean showNav = mWindowManagerService.hasNavigationBar();
if (DEBUG) Log.v(TAG, "hasNavigationBar=" + showNav);
if (showNav) {
createNavigationBar();
}
} catch (RemoteException ex) {
// no window manager? good luck with that
}
...
}
protected void createNavigationBar() {
mNavigationBarView = NavigationBarFragment.create(mContext, (tag, fragment) -> {
mNavigationBar = (NavigationBarFragment) fragment;
if (mLightBarController != null) {
mNavigationBar.setLightBarController(mLightBarController);
}
mNavigationBar.setCurrentSysuiVisibility(mSystemUiVisibility);
});
}
可以看到NavigationBar其实是一个Fragment，循序Fragment的生命周期，这里深入到creat的方法看看具体实现：
public static View create(Context context, FragmentListener listener) {
WindowManager.LayoutParams lp = new WindowManager.LayoutParams(
LayoutParams.MATCH_PARENT, LayoutParams.MATCH_PARENT,
WindowManager.LayoutParams.TYPE_NAVIGATION_BAR,
WindowManager.LayoutParams.FLAG_TOUCHABLE_WHEN_WAKING
| WindowManager.LayoutParams.FLAG_NOT_FOCUSABLE
| WindowManager.LayoutParams.FLAG_NOT_TOUCH_MODAL
| WindowManager.LayoutParams.FLAG_WATCH_OUTSIDE_TOUCH
| WindowManager.LayoutParams.FLAG_SPLIT_TOUCH
| WindowManager.LayoutParams.FLAG_SLIPPERY,
PixelFormat.TRANSLUCENT);
lp.token = new Binder();
lp.setTitle("NavigationBar");
lp.accessibilityTitle = context.getString(R.string.nav_bar);
lp.windowAnimations = 0;
View navigationBarView = LayoutInflater.from(context).inflate(
R.layout.navigation_bar_window, null);
if (DEBUG) Log.v(TAG, "addNavigationBar: about to add " + navigationBarView);
if (navigationBarView == null) return null;
context.getSystemService(WindowManager.class).addView(navigationBarView, lp);
FragmentHostManager fragmentHost = FragmentHostManager.get(navigationBarView);
NavigationBarFragment fragment = new NavigationBarFragment();
fragmentHost.getFragmentManager().beginTransaction()
.replace(R.id.navigation_bar_frame, fragment, TAG)
.commit();
fragmentHost.addTagListener(TAG, listener);
return navigationBarView;
}
可以看到这里设置的LayoutParams中有一个很重要的信息：WindowManager.LayoutParams.TYPE_NAVIGATION_BAR，然后通过context的getSystemService来调用WindowManager的addView方法，这里携带了TYPE_NAVIGATION_BAR进行的addView，在系统部分，除了会像前面两种窗口一样的流程，还会有额外的判断逻辑，保证NavigationBar正常的窗口功能需求。
2.3 Window的更新流程
Window收到更新操作的时候是如何执行流程的呢？这里也来一起看下对应的流程，首先当调用updateViewLayout之后，最终还是会委托给WindowManagerGlobal的updateViewLayout，具体逻辑如下：
public void updateViewLayout(View view, ViewGroup.LayoutParams params) {
if (view == null) {
throw new IllegalArgumentException("view must not be null");
}
if (!(params instanceof WindowManager.LayoutParams)) {
throw new IllegalArgumentException("Params must be WindowManager.LayoutParams");
}
final WindowManager.LayoutParams wparams = (WindowManager.LayoutParams)params;
view.setLayoutParams(wparams);
synchronized (mLock) {
int index = findViewLocked(view, true);
ViewRootImpl root = mRoots.get(index);
mParams.remove(index);
mParams.add(index, wparams);
root.setLayoutParams(wparams, false);
}
}
首先会重新设置View的LayoutParam，然后找到View在View树中的节点，更新mParams列表，最后通过ViewRootImpl中setLayoutParams继续往下执行流程。在setLayoutParams中会调用ViewRootImpl的scheduleTraversals方法，具体逻辑如下：
void scheduleTraversals() {
if (!mTraversalScheduled) {
mTraversalScheduled = true;
mTraversalBarrier = mHandler.getLooper().getQueue().postSyncBarrier();
mChoreographer.postCallback(
Choreographer.CALLBACK_TRAVERSAL, mTraversalRunnable, null);
if (!mUnbufferedInputDispatch) {
scheduleConsumeBatchedInput();
}
notifyRendererOfFramePending();
pokeDrawLockIfNeeded();
}
}
这里通过mChoreographer的postCallback发起了一个回调，在往下将之前，先介绍一下Choreographer，这个是用于接收显示系统的Vsync信号，在下一帧渲染时执行一些操作，这里就是将在下一帧渲染时执行
mTraversalRunnable，具体逻辑如下：
final class TraversalRunnable implements Runnable {
@Override
public void run() {
doTraversal();
}
}
final TraversalRunnable mTraversalRunnable = new TraversalRunnable();
在TraversalRunnable中的run方法里执行了doTraversal，逻辑如下：
void doTraversal() {
if (mTraversalScheduled) {
mTraversalScheduled = false;
mHandler.getLooper().getQueue().removeSyncBarrier(mTraversalBarrier);
if (mProfile) {
Debug.startMethodTracing("ViewAncestor");
}
if (ViewDebugManager.DEBUG_SCHEDULETRAVERSALS)
Trace.traceBegin(Trace.TRACE_TAG_VIEW, "doTraversal");
try {
if(com.journey.system.JourneyDebugFeature.DEBUG_INVALIDATE && (!com.journey.system.JourneyDebugFeature.DEBUG_INVALIDATE_LOW)) {
com.journey.system.JourneyDebugFeature.enableLogViewInvalidate(false);}
performTraversals();
} finally {
if (ViewDebugManager.DEBUG_SCHEDULETRAVERSALS) Trace.traceEnd(Trace.TRACE_TAG_VIEW);
}
if (mProfile) {
Debug.stopMethodTracing();
mProfile = false;
}
}
}
最终调用了performTraversals方法，该方法就是让View树执行View的工作流程，逻辑如下：
private void performTraversals() {
...
relayoutResult = relayoutWindow(params, viewVisibility, insetsPending);
...
if (!mStopped || mReportNextDraw) {
boolean focusChangedDueToTouchMode = ensureTouchModeLocally(
(relayoutResult&WindowManagerGlobal.RELAYOUT_RES_IN_TOUCH_MODE) != 0);
if (focusChangedDueToTouchMode || mWidth != host.getMeasuredWidth()
|| mHeight != host.getMeasuredHeight() || contentInsetsChanged ||
updatedConfiguration) {
int childWidthMeasureSpec = getRootMeasureSpec(mWidth, lp.width);
int childHeightMeasureSpec = getRootMeasureSpec(mHeight, lp.height);
// Ask host how big it wants to be
performMeasure(childWidthMeasureSpec, childHeightMeasureSpec);
}
...
if (didLayout) {
performLayout(lp, mWidth, mHeight);
...
}
...
if (!cancelDraw && !newSurface) {
if (mPendingTransitions != null && mPendingTransitions.size() > 0) {
for (int i = 0; i < mPendingTransitions.size(); ++i) {
mPendingTransitions.get(i).startChangingAnimations();
}
mPendingTransitions.clear();
}
performDraw();
}
...
}
这里需要关注以下几个方法：1.relayoutWindow方法会最终调用IWindowSession的relayout方法让WMS来更新Window视图，2.performMeasure、performLayout以及performDraw分别对应者view的measure、Layout以及draw操作，这样同时执行了Window视图的更新，以及View的工作流程，最后实现了Window的更新。
到这里，Window的添加和更新操作Window到WinddowManger以及WindowManager如何向WMS通讯的流程已经梳理完毕，至于删除操作我们将在WMS解析的章节里面进一步详细介绍。
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