Android绘制流程窗口启动流程分析下

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

1. 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。
2. 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。
3. 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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