Window是一个抽象类，具体的实现是PhoneWindow。窗口的本质是什么呢？其实就是一块显示区域，在 Android 中就是绘制的画布：Surface，当一块 Surface 显示在屏幕上时，就是用户所看到的窗口了。WindowManagerService 添加一个窗口的过程，其实就是 WindowManagerService 为其分配一块 Surface 的过程，一块块的 Surface 在 WindowManagerService 的管理下有序的排列在屏幕上，Android 才得以呈现出多姿多彩的界面。
WindowManager继承自ViewManager
public interface ViewManager
{
/**
* Assign the passed LayoutParams to the passed View and add the view to the window.
* Throws {@link android.view.WindowManager.BadTokenException} for certain programming
* errors, such as adding a second view to a window without removing the first view.
*
Throws {@link android.view.WindowManager.InvalidDisplayException} if the window is on a
* secondary {@link Display} and the specified display can't be found
* (see {@link android.app.Presentation}).
* @param view The view to be added to this window.
* @param params The LayoutParams to assign to view.
*/
public void addView(View view, ViewGroup.LayoutParams params);
public void updateViewLayout(View view, ViewGroup.LayoutParams params);
public void removeView(View view);
}
每个Window对应着一个View和一个ViewRootImpl。Window和View通过ViewRootImpl来建立联系。view才是Window存在的实体。对window的访问必须通过WindowManager。
WindowManager是一个接口。真正的实现是WindowManagerImpl。但是WindowManagerImpl又交给WindowManagerGlobal来处理,
分析global的添加View的过程
public void addView(View view, ViewGroup.LayoutParams params,
Display display, Window parentWindow) {
//检查参数是否适合，调整布局参数
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ViewRootImpl，并将参数添加到列表中
root = new ViewRootImpl(view.getContext(), display);
view.setLayoutParams(wparams);
mViews.add(view);
mRoots.add(root);
mParams.add(wparams);
}
// do this last because it fires off messages to start doing things
try {
//方法内部会调用requestLayout来实现刷新请求
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;
}
}
WindowManagerGlobal维护着和Window操作相关的三个列表，在添加，更新，删除的时候都会涉及到他们，View列表mViews,布局参数列表mParams,ViewRootImpl列表。
再看ViewRootImpl的setView方法
public void setView(View view, WindowManager.LayoutParams attrs, View panelParentView) {
synchronized (this) {
.....
// Schedule the first layout -before- adding to the window
// manager, to make sure we do the relayout before receiving
// any other events from the system.
requestLayout(); //异步刷新
if ((mWindowAttributes.inputFeatures
& WindowManager.LayoutParams.INPUT_FEATURE_NO_INPUT_CHANNEL) == 0) {
mInputChannel = new InputChannel();
}
mForceDecorViewVisibility = (mWindowAttributes.privateFlags
& PRIVATE_FLAG_FORCE_DECOR_VIEW_VISIBILITY) != 0;
try {
mOrigWindowType = mWindowAttributes.type;
mAttachInfo.mRecomputeGlobalAttributes = true;
collectViewAttributes();
//通过windowSession完成window的添加，内部会windowManagerService来实现window的添加
res = mWindowSession.addToDisplay(mWindow, mSeq, mWindowAttributes,
getHostVisibility(), mDisplay.getDisplayId(),
mAttachInfo.mContentInsets, mAttachInfo.mStableInsets,
mAttachInfo.mOutsets, mInputChannel);
} catch (RemoteException e) {
...
} finally {
if (restore) {
attrs.restore();
}
}
....
}
}
所以说ViewRoot是WindowManagerService和DecorView的纽带。ViewRootImpl 负责管理View树，负责与wms通信
Activity的window添加过程
Activity的启动过程很复杂。最终由ActivityThread的performLaunchActivity完成启动流程，方法内部会通过类加载器创建Activity的实例对象，并调用attach。在attach中，系统会创建window对象，并设置回调
mWindow = PolicyManager.makeNewWindow(this)；//PolicyManager的真正实现是Policy类，返回的是一个PhoneWindow
mWindow.setCallback(this);
mWindow.setOnWindowDismissedCallback(this);
mWindow.getLayoutInflater().setPrivateFactory(this);
mWindow.setWindowManager(...);
Callback 接口中的方法很多，有几个是我们非常熟悉的，如 onAttachedToWindow、onDetachedFromWindow、dispatchTouchEvent