原文转载：https://www.cnblogs.com/tiger-wang-ms/p/6517048.html

三、handleResumeActivity()流程

在文章结尾贴出的第一段AcitityThread.handleLauncherActivity()办法的代码中，执行完performLaunchAcitity()创立好Acitivity后，便会执行到handleResumeActivity()办法，该办法代码如下。

final void handleResumeActivity(IBinder token,

boolean clearHide, boolean isForward, boolean reallyResume, int seq, String reason) {

...// TODO Push resumeArgs into the activity for consideration

// 该办法执行过程中会调用到Acitity的onResume()办法，返回的ActivityClientRecord对象形容的即是创立好的Activity　　　　　r = performResumeActivity(token, clearHide, reason);

if (r != null) {

final Activity a = r.activity;//返回之前创立的Acitivty

if (localLOGV) Slog.v(

TAG, "Resume " + r + " started activity: " +

a.mStartedActivity + ", hideForNow: " + r.hideForNow

+ ", finished: " + a.mFinished);

final int forwardBit = isForward ?

WindowManager.LayoutParams.SOFT_INPUT_IS_FORWARD_NAVIGATION : 0;

// If the window hasn't yet been added to the window manager,

// and this guy didn't finish itself or start another activity,

// then go ahead and add the window.　　　　　　　// 判断该Acitivity是否可见，mStartedAcitity记录的是一个Activity是否还处于启动状态　　　　　　　// 如果还处于启动状态则mStartedAcitity为true，示意该activity还未启动好，则该Activity还不可见　　　　　　　boolean willBeVisible = !a.mStartedActivity;　　　　　　　// 如果启动的组建不是全屏的，mStartedActivity也会是true，此时仍然须要willBeVisible为true以下的if逻辑就是针对这种状况的校对

if (!willBeVisible) {

try {

willBeVisible = ActivityManagerNative.getDefault().willActivityBeVisible(

a.getActivityToken());

} catch (RemoteException e) {

throw e.rethrowFromSystemServer();

}

}

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;

l.softInputMode |= forwardBit;　　　　　　　　　 //PreserverWindow，个别指主题换了或者configuration变了状况下的Acitity疾速重启机制

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 && !a.mWindowAdded) {

a.mWindowAdded = true;　　　　　　　　　　　　//调用了WindowManagerImpl的addView办法

wm.addView(decor, l);

}

...

}

重点来看wm.addView()办法，该办法中的decor参数为Acitity对应的Window中的视图DecorView，wm为在创立PhoneWindow是创立的WindowManagerImpl对象，该对象的addView办法理论调用到到是单例对象WindowManagerGlobal的addView办法(前文有提到)。在看addView代码前，我先来看看WindowManagerGlobal对象成员变量。

private static WindowManagerGlobal sDefaultWindowManager;

private static IWindowManager sWindowManagerService;

private static IWindowSession sWindowSession;

private final Object mLock = new Object();

private final ArrayList mViews = new ArrayList();

private final ArrayList mRoots = new ArrayList();

private final ArrayList mParams =

new ArrayList();

private final ArraySet mDyingViews = new ArraySet();

三个成员变量mViews、mRoots和mParams别离是类型为View、ViewRootImpl和WindowManager.LayoutParams的数组。这里有这样的逻辑关系，每个View都对应着惟一的一个ViewRootImpl和WindowManager.LayoutRarams，即是1:1:1的关系。这三个数组长度始终保持统一，并且在同一个地位上寄存的是相互关联的View、ViewRootImpl和WindowManager.LayoutParams对象。此外还有一个成员变量mDyView，保留的则是曾经不须要但还未被零碎会收到View。

View与LayoutParams比拟好了解，那ViewRootImpl对象的作用是什么呢？首先WindowManagerImpl是作为治理类，就像主管一样，依据Acitity和Window的调用申请，找到适合的做事的人；DecorView自身是FrameworkLayout，本事是一个View，所示意的是一种动态的构造；所以这里就须要一个真正做事的人，那就是ViewRootImpl类的工作。总结来讲ViewRootImpl的性能如下

实现了绘制过程。在ViewRootImpl类中，实现了perfromMeasure()、performDraw()、performLayout()等绘制相干的办法。

与零碎服务进行交互，例如与AcitityManagerSerivice，DisplayService、AudioService等进行通信，保障了Acitity相干性能等失常运行。

触屏事件等散发逻辑的实现

接下来咱们进入WindowManagerGlobal.addView()办法的代码。

public void addView(View view, ViewGroup.LayoutParams params,

Display display, Window parentWindow) {

...

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.　　　　　　　// 如果以后增加的是一个子视图，则还须要找他他的父视图　　　　　　　//这里咱们剖析的是增加DecorView的逻辑，没有父视图，故不会走到这里，panelParentView为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);

//保留相互对应的View、ViewRootImpl、WindowManager.LayoutParams到数组中

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;

}

}

}

关注代码中加粗的两个办法，首先会创立一个ViewRootImpl对象，而后调用ViewRootImpl.setView办法，其中panelParentView在addView参数为DecorView是为null。进入ViewRootImpl.setView()代码。

public void setView(View view, WindowManager.LayoutParams attrs, View panelParentView) {

synchronized (this) {

if (mView == null) {　　　　　　　　　 //初始化成员变量mView、mWindowAttraibutes　　　　　　　　　 //mAttachInfo是View类的一个外部类AttachInfo类的对象 //该类的次要作用就是贮存一组当View attach给它的父Window的时候Activity各种属性的信息 mView = view;

mAttachInfo.mDisplayState = mDisplay.getState();

mDisplayManager.registerDisplayListener(mDisplayListener, mHandler);

mViewLayoutDirectionInitial = mView.getRawLayoutDirection();

mFallbackEventHandler.setView(view);

mWindowAttributes.copyFrom(attrs);

... //持续初始化一些变量，蕴含针对panelParentView不为null时的父窗口的一些解决

mAdded = true;

// Schedule the first layout -before- adding to the window

// manager, to make sure we do the relayout before receiving

// any other events from the system.　　　　　　　　　　// 这里调用异步刷新申请，最终会调用performTraversals办法来实现View的绘制　　　　　　　　　　requestLayout();

if ((mWindowAttributes.inputFeatures

& WindowManager.LayoutParams.INPUT_FEATURE_NO_INPUT_CHANNEL) == 0) {

mInputChannel = new InputChannel();

}

mForceDecorViewVisibility = (mWindowAttributes.privateFlags

& PRIVATE_FLAG_FORCE_DECOR_VIEW_VISIBILITY) != 0;

try {

mOrigWindowType = mWindowAttributes.type;

mAttachInfo.mRecomputeGlobalAttributes = true;

collectViewAttributes();

res = mWindowSession.addToDisplay(mWindow, mSeq, mWindowAttributes,

getHostVisibility(), mDisplay.getDisplayId(),

mAttachInfo.mContentInsets, mAttachInfo.mStableInsets,

mAttachInfo.mOutsets, mInputChannel);

} catch (RemoteException e) {

mAdded = false;

mView = null;

mAttachInfo.mRootView = null;

mInputChannel = null;

mFallbackEventHandler.setView(null);

unscheduleTraversals();

setAccessibilityFocus(null, null);

throw new RuntimeException("Adding window failed", e);

} finally {

if (restore) {

attrs.restore();

}

}

...

}

}

}

相干变量初始化实现后，便会将mAdded设置为true，示意ViewRootImpl与setView传入的View参数曾经做好了关联。之后便会调用requestLayout()办法来申请一次异步刷新，该办法起初又会调用到performTraversals()办法来实现view到绘制工作。留神到这里尽管实现了绘制的工作，然而咱们创立Activity的源头是AMS中发动的，咱们从一开始创立Acitivity到绝对应的Window、DecorView这一大套对象时，还并未与AMS过程进行反馈。所以之后便会调用mWindowSession.addToDisplay()办法会执行IPC的跨过程通信，最终调用到AMS中的addWindow办法来在零碎过程中执行相干加载Window的操作。

点击下方链接收费获取Android进阶材料:

https://shimo.im/docs/tXXKHgdjPYj6WT8d/