前言

在上一篇文章中我们主要分析了android.app.ActivityThread的main函数以及setContentView。另外我们还稍微分析了一下我们自己的源码，通过WindowManager添加View。我们知道调用setContentView把我们自己的xml布局添加到了DecorView ID为ID_ANDROID_CONTENT的布局后，最终还是会调用WindowManager.addView把DecorView加入PhoneWindow。到这里呢，我们把流程梳理一下。还是上图：

相信读者根据上图再结合前面所讲的内容应该对Activity的创建和显示有了初步的认识。那么本章我们来继续讲Activity的显示。该注意的是本系列并不意在带领读者去看清每一步具体的源码。在前面的文章中我也很少贴出源码。本系列文章意在让读者对Android系统有个更整体的把握。我所写的每一章知识都有可能在实际工作中用到。就如前面所讲解的Android下的进程问题以及Activity的生命周期以及本章要讲解的View的五大过程的基础ViewRootImpl。而理解View的五大过程（一般文章里都是三大过程）以及View的事件体系是更好的去自定义View的基础。

WindowManager 与 ViewRootImpl

WindowManager.addView()源码解析

public interface WindowManager extends ViewManager {    //这里我们只列出了一部分函数，但是并没有addView、updateViewLayout、removeView这三个函数    public Display getDefaultDisplay();    public void removeViewImmediate(View view);    ...}

好吧，果然没有这么简单，WindowManager是个接口，而且在其方法中没有找到addView方法，那么我们只能看看ViewManager了

public interface ViewManager{    public void addView(View view, ViewGroup.LayoutParams params);    public void updateViewLayout(View view, ViewGroup.LayoutParams params);    public void removeView(View view);}

还好是找到了，ViewManager没有再继承其他接口了。(要不然真不知道要找到什么时候去。)

既然WindowManager是个接口，那肯定要找它的实现类了。（在这里安利一个比较简单的方法，在Android Studio中）

public final class WindowManagerImpl implements WindowManager {    private final WindowManagerGlobal mGlobal = WindowManagerGlobal.getInstance();    private final Context mContext;    private final Window mParentWindow;    private IBinder mDefaultToken;    public WindowManagerImpl(Context context) {        this(context, null);    }    private WindowManagerImpl(Context context, Window parentWindow) {        mContext = context;        mParentWindow = parentWindow;    }    public WindowManagerImpl createLocalWindowManager(Window parentWindow) {        return new WindowManagerImpl(mContext, parentWindow);    }    public WindowManagerImpl createPresentationWindowManager(Context displayContext) {        return new WindowManagerImpl(displayContext, mParentWindow);    }    /**     * Sets the window token to assign when none is specified by the client or     * available from the parent window.     *     * @param token The default token to assign.     */    public void setDefaultToken(IBinder token) {        mDefaultToken = token;    }    @Override    public void addView(@NonNull View view, @NonNull ViewGroup.LayoutParams params) {        applyDefaultToken(params);        mGlobal.addView(view, params, mContext.getDisplay(), mParentWindow);    }    @Override    public void updateViewLayout(@NonNull View view, @NonNull ViewGroup.LayoutParams params) {        applyDefaultToken(params);        mGlobal.updateViewLayout(view, params);    }    private void applyDefaultToken(@NonNull ViewGroup.LayoutParams params) {        // Only use the default token if we don't have a parent window.        if (mDefaultToken != null && mParentWindow == null) {            if (!(params instanceof WindowManager.LayoutParams)) {                throw new IllegalArgumentException("Params must be WindowManager.LayoutParams");            }            // Only use the default token if we don't already have a token.            final WindowManager.LayoutParams wparams = (WindowManager.LayoutParams) params;            if (wparams.token == null) {                wparams.token = mDefaultToken;            }        }    }    @Override    public void removeView(View view) {        mGlobal.removeView(view, false);    }    @Override    public void removeViewImmediate(View view) {        mGlobal.removeView(view, true);    }    @Override    public void requestAppKeyboardShortcuts(            final KeyboardShortcutsReceiver receiver, int deviceId) {        IResultReceiver resultReceiver = new IResultReceiver.Stub() {            @Override            public void send(int resultCode, Bundle resultData) throws RemoteException {                List
    
      result =                        resultData.getParcelableArrayList(PARCEL_KEY_SHORTCUTS_ARRAY);                receiver.onKeyboardShortcutsReceived(result);            }        };        try {            WindowManagerGlobal.getWindowManagerService()                .requestAppKeyboardShortcuts(resultReceiver, deviceId);        } catch (RemoteException e) {        }    }    @Override    public Display getDefaultDisplay() {        return mContext.getDisplay();    }}

WindowManagerImpl的源码如上所示，我们可以看到WindowManagerImpl的addView方法，WindowManagerImpl把工作交给了WindowManagerGlobal

WindowManagerGlobal

/**WindowManagerGlobal 源码比较长，这里我们只列出了一部分*/public final class WindowManagerGlobal {    private WindowManagerGlobal() {    }    public static void initialize() {        getWindowManagerService();    }    public static WindowManagerGlobal getInstance() {        synchronized (WindowManagerGlobal.class) {            if (sDefaultWindowManager == null) {                sDefaultWindowManager = new WindowManagerGlobal();            }            return sDefaultWindowManager;        }    }    public static IWindowManager getWindowManagerService() {        synchronized (WindowManagerGlobal.class) {            if (sWindowManagerService == null) {                sWindowManagerService = IWindowManager.Stub.asInterface(                        ServiceManager.getService("window"));                try {                    if (sWindowManagerService != null) {                        ValueAnimator.setDurationScale(                                sWindowManagerService.getCurrentAnimatorScale());                    }                } catch (RemoteException e) {                    throw e.rethrowFromSystemServer();                }            }            return sWindowManagerService;        }    }    public static IWindowSession getWindowSession() {        synchronized (WindowManagerGlobal.class) {            if (sWindowSession == null) {                try {                    InputMethodManager imm = InputMethodManager.getInstance();                    IWindowManager windowManager = getWindowManagerService();                    sWindowSession = windowManager.openSession(                            new IWindowSessionCallback.Stub() {                                @Override                                public void onAnimatorScaleChanged(float scale) {                                    ValueAnimator.setDurationScale(scale);                                }                            },                            imm.getClient(), imm.getInputContext());                } catch (RemoteException e) {                    throw e.rethrowFromSystemServer();                }            }            return sWindowSession;        }    }    public static IWindowSession peekWindowSession() {        synchronized (WindowManagerGlobal.class) {            return sWindowSession;        }    }    //addView方法    public void addView(View view, ViewGroup.LayoutParams params,            Display display, Window parentWindow) {        ...  //参数检查        final WindowManager.LayoutParams wparams = (WindowManager.LayoutParams) params;        if (parentWindow != null) {            //① 如果当前窗口需要被添加为另一个窗口的附属窗口(子窗口)，则需要父窗口视自己的情况对当前窗口的布局参数进行调整            parentWindow.adjustLayoutParamsForSubWindow(wparams);        }        ViewRootImpl root;        View panelParentView = null;               int index = findViewLocked(view, false);          if (index >= 0) {              if (mDyingViews.contains(view)) {                  mRoots.get(index).doDie();              } else {              //同一个View不允许被添加2次                  throw new IllegalStateException("View " + view                          + " has already been added to the window manager.");              }          }        //② 创建一个ViewRootImpl对象并保存在root变量中         root = new ViewRootImpl(view.getContext(), display);         view.setLayoutParams(wparams);        //③ 保存作为窗口的控件、布局参数以及新建的ViewRootImpl         mViews.add(view);         mRoots.add(root);         mParams.add(wparams);         // do this last because it fires off messages to start doing things         try {             // ④ 将作为窗口的控件设置给ViewRootImpl.这个动作将导致ViewRootImpl向WMS添加新的窗口、申请Surface以及托管控件在Surface上的重绘工作。这才是真正意义上完成了窗口的添加工作。             root.setView(view, wparams, panelParentView);         } catch (RuntimeException e) {             // BadTokenException or InvalidDisplayException, clean up.             if (index >= 0) {                 removeViewLocked(index, true);             }             throw e;         }        }    }    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);        }    }    public void removeView(View view, boolean immediate) {        if (view == null) {            throw new IllegalArgumentException("view must not be null");        }        synchronized (mLock) {            int index = findViewLocked(view, true);            View curView = mRoots.get(index).getView();            removeViewLocked(index, immediate);            if (curView == view) {                return;            }            throw new IllegalStateException("Calling with view " + view                    + " but the ViewAncestor is attached to " + curView);        }    }   }

我们可以看到WindowManagerGlobal的私有构造函数以及getInstance()这个熟悉的静态方法名字。可以看出WindowManagerGlobal是个典型的单例。

WindowManagerGlobal 的addView方法并不复杂，其主要的关键点我们已经标注并写了注释。也就是说WindowManagerGlobal的职责如下：

同意管理整个进程中所有窗口的信息。包括控件、布局参数以及ViewRootImpl这三个元素。（这一点从第③个注释可以看出）

WindowManagerGlobal将窗口的创建、销毁、布局更新等任务交给了ViewRootImpl完成。

本篇总结

本篇文章分析了WindowManager的addView的过程，WindowManager是个接口，它的实现类是WindowManagerImpl类，而WindowManagerImpl又把相关逻辑交给了WindowManagerGlobal处理。WindowManagerGlobal是个单例类，它在进程中只存在一个实例，是它内部的addView方法最终创建了我们的核心类ViewRootImpl。ViewRootImpl实现了ViewParent接口，作为整个控件树的根部，它是控件树正常运作的动力所在，控件的测量、布局、绘制以及输入事件的派发处理窦世友ViewRootImpl出发。它是WindowManagerGlobal的实际工作者。

下篇预告

在下一篇文章中我们将深入介绍ViewRootImpl的工作流程。测量、布局、以及绘制。

参考博文

此致，敬礼

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