该文章是一个系列文章，是本人在Android开发的漫漫长途上的一点感想和记录，如果能给各位看官带来一丝启发或者帮助，那真是极好的。
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<KeyboardShortcutGroup> 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
