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<View> mViews = new ArrayList<View>(); private final ArrayList<ViewRootImpl> mRoots = new ArrayList<ViewRootImpl>(); private final ArrayList<WindowManager.LayoutParams> mParams = new ArrayList<WindowManager.LayoutParams>(); private final ArraySet<View> mDyingViews = new ArraySet<View>();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。
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