对于Activity，在ActivityThread.java在handleLaunchActivity会调用performLaunchActivity，而performLaunchActivity则调用Activity中的attach函数，实现创建window(实际是PhoneWindow)：
Activity.java
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) {
//创建window
mWindow = PolicyManager.makeNewWindow(this);
mWindow.setCallback(this);
mWindow.getLayoutInflater().setPrivateFactory(this);
if (info.softInputMode != WindowManager.LayoutParams.SOFT_INPUT_STATE_UNSPECIFIED) {
mWindow.setSoftInputMode(info.softInputMode);
}
if (info.uiOptions != 0) {
mWindow.setUiOptions(info.uiOptions);
}
//获取WindowManager
mWindow.setWindowManager(null, mToken, mComponent.flattenToString(),
(info.flags & ActivityInfo.FLAG_HARDWARE_ACCELERATED) != 0);
mWindowManager = mWindow.getWindowManager();
}
PolicyManager.java
public static Window makeNewWindow(Context context) {
//使用sPolicy来创建window
return sPolicy.makeNewWindow(context);
}
这里的sPolicy定义是：private static final IPolicy sPolicy;
那么，如何初始化？
private static final String POLICY_IMPL_CLASS_NAME =
static {
// 获取Policy这个class并实例化
try {
Class policyClass = Class.forName(POLICY_IMPL_CLASS_NAME);
sPolicy = (IPolicy)policyClass.newInstance();
}
}
再往下：
Policy.java
public class Policy implements IPolicy {
public Window makeNewWindow(Context context) {
/*可见，activity.attach中的PolicyManager.makeNewWindow(this)是新建一个PhoneWindow
*context则是Activity中实现的ContextImpl实例
*而PhoneWindow是window的子类，故而可以赋给window
*/
return new PhoneWindow(context);
}
……
}
由Policy的定义可知，Policy implement IPolicy，并且实现了它定义的接口。
/*至此，实现了创建一个PhoneWindow*/
接着Activity.attach往下：
//设置window的Callback，Activity是实现了Window.Callback的接口的
mWindow.setCallback(this);
mWindow.getLayoutInflater().setPrivateFactory(this);
//设置soft input mode
if (info.softInputMode != WindowManager.LayoutParams.SOFT_INPUT_STATE_UNSPECIFIED) {
mWindow.setSoftInputMode(info.softInputMode);
}
if (info.uiOptions != 0) {
mWindow.setUiOptions(info.uiOptions);
}
我们回到最初，我们说过，在ActivityThread中会在performLaunchActivity之后判断是否成功，并真正调用handleResumeActivity();
ActivityThread.java
final void handleResumeActivity(IBinder token, boolean clearHide, boolean isForward) {
ActivityClientRecord r = performResumeActivity(token, clearHide);
//这个layoutParams是在ActivityClientRecord 这里的。
WindowManager.LayoutParams l = r.window.getAttributes();
……
/*
*r是ActivityClientRecord，在performResumeActivity之前并没有将window加入到r中
*那么，activity如何创建并且是如何加入到这个activityClientRecord中的呢？
*/
if (r.window == null && !a.mFinished && willBeVisible) {
//在activity的attach函数中创建的activity的window赋给r.window
r.window = r.activity.getWindow();
//我们知道attach创建的是PhoneWindow，那PhoneWindow中DecorView如何创建的？
View decor = r.window.getDecorView();
decor.setVisibility(View.INVISIBLE);
//WindowManager是ViewManager的子类
ViewManager wm = a.getWindowManager();
WindowManager.LayoutPar