AndroidR WindowToken（1）
class WindowContainer<E extends WindowContainer> extends ConfigurationContainer<E>
implements Comparable<WindowContainer>
class RootWindowContainer extends WindowContainer<DisplayContent>
class DisplayContent extends WindowContainer<DisplayContent.DisplayChildWindowContainer>
class WindowState extends WindowContainer<WindowState>
class WindowToken extends WindowContainer<WindowState>
final class ActivityRecord extends WindowToken
class Task extends WindowContainer<WindowContainer>
class ActivityStack extends Task
参考:https://www.kancloud.cn/alex_wsc/android-deep3/416391
final class ActivityRecord extends WindowToken
在ActivityRecord的构造方法中，先调用父类WindowToken的构造函数，得到其WindowToken
因此，ActivityRecord的apptoken（IApplicationToken.Stub）是等价于WindowToken的（强制类型转换）
super(_service.mWindowManager, new Token(_intent).asBinder(), TYPE_APPLICATION, true,
null /* displayContent */, false /* ownerCanManageAppTokens */);
mAtmService = _service;
appToken = (Token) token;
info = aInfo;
mUserId = UserHandle.getUserId(info.applicationInfo.uid);
packageName = info.applicationInfo.packageName;
对于显示组件（客户端）而言的Token，是任意一个Binder的实例，对显示组件（客户端）来说仅仅是一个创建窗口的令牌，没有其他的含义。
Token(Intent intent) {
name = intent.getComponent().flattenToShortString();
tokenString = "Token{" + Integer.toHexString(System.identityHashCode(this)) + "}";
}
WindowToken由token和WindowType来区分，已没有AppWindowToken这个类。添加 WindowToken，也是根据WindowType来添加
class WindowToken extends WindowContainer<WindowState> {
// The actual token.
final IBinder token;
// The type of window this token is for, as per WindowManager.LayoutParams.
final int windowType;
WindowState是WMS中的窗口实例，其mToken保存了窗口令牌，其ActivityRecord保存了对应的Activity（如果是应用窗口的话，不是应用窗口，则为null）
class WindowState extends WindowContainer<WindowState>
WindowToken mToken;
// The same object as mToken if this is an app window and null for non-app windows.
ActivityRecord mActivityRecord;
WindowToken的构造方法
WindowToken(WindowManagerService service, IBinder _token, int type, boolean persistOnEmpty,
DisplayContent dc, boolean ownerCanManageAppTokens, int ownerUid,
boolean roundedCornerOverlay, boolean fromClientToken) {
super(service);
token = _token;
windowType = type;
mPersistOnEmpty = persistOnEmpty;
mOwnerCanManageAppTokens = ownerCanManageAppTokens;
mOwnerUid = ownerUid;
mRoundedCornerOverlay = roundedCornerOverlay;
mFromClientToken = fromClientToken;
if (dc != null) {
dc.addWindowToken(token, this);
}
最后，是在DisplayContent中添加WindowToken
//DisplayContent.java
void addWindowToken(IBinder binder, WindowToken token) {
mTokenMap.put(binder, token);
//如果调用ActivityRecord#asActivityRecord为空，说明其不是Activity的Token
if (token.asActivityRecord() == null) {
总结：ActivityRecord----->apptoken----->WindowToken----->WindowState
可以由WindowState来处理ActivityRecord的可见性等问题
