Android View的重绘过程之WindowManager的addView方法

博客首页：http://www.cnblogs.com/kezhuang/p/

关于Activity的contentView的构建过程，我在我的博客中已经分析过了，不了解的可以去看一下

《[Android FrameWork 6.0源码学习] Window窗口类分析》

本章博客是接着上边那篇博客分析，目的是为了引出分析ViewRootImpl这个类。现在只是分析完了Window和ActivityThread的调用过程

从ActivityThread到WindowManager再到ViewRootImpl这块还属于空白部分，所以要补这篇博客

在上篇博客的末尾提到最后是由WindowManager的addView来请求显示界面，那么我们接着分析

WindowManager这是一个接口，他继承了ViewManager这个接口，所以具有管理View的能力

WindowManager这个实例是通过 Activity.getWindowManager 方法获取的，我们先找到他的实例，在逐渐去看addView函数

    public WindowManager getWindowManager() {
        return mWindowManager;
    }

Activity中是这样定义的该函数，返回了mWindowManager对像，接下来找一下赋值mWindowManager对象的地方

    final void attach(Context context, ActivityThread aThread,
            Instrumentation instr, IBinder token, int ident,
            Application application, Intent intent, ActivityInfo info,
            CharSequence title, Activity parent, String id,
            NonConfigurationInstances lastNonConfigurationInstances,
            Configuration config, String referrer, IVoiceInteractor voiceInteractor) {

        mWindow = new PhoneWindow(this);
        mWindow.setCallback(this);
        mWindow.setOnWindowDismissedCallback(this);
        mWindow.getLayoutInflater().setPrivateFactory(this);
        mWindow.setWindowManager(
                (WindowManager)context.getSystemService(Context.WINDOW_SERVICE),
                mToken, mComponent.flattenToString(),
                (info.flags & ActivityInfo.FLAG_HARDWARE_ACCELERATED) != 0);
        if (mParent != null) {
            mWindow.setContainer(mParent.getWindow());
        }
        mWindowManager = mWindow.getWindowManager();
    }

我们看到在Activity初始化时候调用的attach方法中赋值了mWindowManager方法，但是这个值是从mWindow对象中获取到的，我们进入看一下

    public WindowManager getWindowManager() {
        return mWindowManager;
    }

在Window中也是这样定义的，返回mWindowManager

    public void setWindowManager(WindowManager wm, IBinder appToken, String appName,
            boolean hardwareAccelerated) {
        mAppToken = appToken;
        mAppName = appName;
        mHardwareAccelerated = hardwareAccelerated
                || SystemProperties.getBoolean(PROPERTY_HARDWARE_UI, false);
        if (wm == null) {
            wm = (WindowManager)mContext.getSystemService(Context.WINDOW_SERVICE);
        }
        mWindowManager = ((WindowManagerImpl)wm).createLocalWindowManager(this);
    }

Window中的mWindowManager是在setWindowManager中创建而来，而这个setWindowManager其实是在Activity的attach方法中调用
可以看到其实就是用的系统服务WindowManager强转成WindowManagerImpl之后又调用了createLocalWindowManager方法得到的对象

    public WindowManagerImpl createLocalWindowManager(Window parentWindow) {
        return new WindowManagerImpl(mDisplay, parentWindow);
    }

这个方法也很简单，就是new了一下WindowManagerImpl

OK了，到现在可以知道WindowManager的实现类为WindowManagerImpl，那么我们继续分析它实现的addView方法

    @Override
    public void addView(@NonNull View view, @NonNull ViewGroup.LayoutParams params) {
        applyDefaultToken(params);
        mGlobal.addView(view, params, mDisplay, mParentWindow);
    }

该方法定义在WindowManagerImpl中，mGlobal为WindowManagerGlobal对象，是一个系统单例对象

    public void addView(View view, ViewGroup.LayoutParams params,
            Display display, Window parentWindow) {
        if (view == null) {
            throw new IllegalArgumentException("view must not be null");
        }
        if (display == null) {
            throw new IllegalArgumentException("display must not be null");
        }
        if (!(params instanceof WindowManager.LayoutParams)) {
            throw new IllegalArgumentException("Params must be WindowManager.LayoutParams");
        }

        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);
                    }
                }
            }

            //创建了一个新的ViewRootImpl对象出来
            root = new ViewRootImpl(view.getContext(), display);

            view.setLayoutParams(wparams);
            //为当前界面保存ViewRootImpl和view还有添加的Layout参数
            mViews.add(view);
            mRoots.add(root);
            mParams.add(wparams);
        }
        // do this last because it fires off messages to start doing things
        try {
        //调用ViewRootImpl中的setView方法，准备进行View的重绘流程，并且绘制到界面上
            root.setView(view, wparams, panelParentView);
        } catch (RuntimeException e) {
            // BadTokenException or InvalidDisplayException, clean up.
            synchronized (mLock) {
                final int index = findViewLocked(view, false);
                if (index >= 0) {
                    removeViewLocked(index, true);
                }
            }
            throw e;
        }
    }

这篇博客到这就结束了，接下来我总结下上边的流程
1.Activity初始化的时候创建了一个WindowManager对象(和系统的WindowManager服务还有点区别)
2.利用这个Activity专属的WindowManager对象请求添加一个View到当前界面上
3.WindowManager找到自己的实现类WindowManagerImpl，然后在委托给系统单例类WindowManagerGlobal处理
4.WindowManagerGlobal会创建一个ViewRootImpl对象出来
5.ViewRootImpl对象调用setView方法，然后进行界面重绘最后交给Surface进行界面展示

Ok了，很清晰的分析出了从WindowManager到ViewRootImpl的过程，接下来就可以分析ViewRootImpl.setView和ViewRootImpl的performTraversals方法了