IWindow是很重要的，官方介绍是API back to a client window that the Window Manager uses to inform it of interesting things happening. 也就是说是是用于WMS回调客户端的，当窗口有一些改变时，WMS及时调用客户端接口，让客户端窗口立即更新。

IWindow.aidl - OpenGrok cross reference for /frameworks/base/core/java/android/view/IWindow.aidl

/*** API back to a client window that the Window Manager uses to inform it of* interesting things happening.** {@hide}*/
oneway interface IWindow {/*** ===== NOTICE =====* The first method must remain the first method. Scripts* and tools rely on their transaction number to work properly.*//*** Invoked by the view server to tell a window to execute the specified* command. Any response from the receiver must be sent through the* specified file descriptor.*/void executeCommand(String command, String parameters, in ParcelFileDescriptor descriptor);void resized(in ClientWindowFrames frames, boolean reportDraw,in MergedConfiguration newMergedConfiguration, in InsetsState insetsState,boolean forceLayout, boolean alwaysConsumeSystemBars, int displayId,int syncSeqId, boolean dragResizing);/*** Called when this window retrieved control over a specified set of insets sources.*/void insetsControlChanged(in InsetsState insetsState, in InsetsSourceControl[] activeControls);/*** Called when a set of insets source window should be shown by policy.** @param types internal insets types (WindowInsets.Type.InsetsType) to show* @param fromIme true if this request originated from IME (InputMethodService).* @param statsToken the token tracking the current IME show request or {@code null} otherwise.*/void showInsets(int types, boolean fromIme, in @nullable ImeTracker.Token statsToken);/*** Called when a set of insets source window should be hidden by policy.** @param types internal insets types (WindowInsets.Type.InsetsType) to hide* @param fromIme true if this request originated from IME (InputMethodService).* @param statsToken the token tracking the current IME hide request or {@code null} otherwise.*/void hideInsets(int types, boolean fromIme, in @nullable ImeTracker.Token statsToken);void moved(int newX, int newY);void dispatchAppVisibility(boolean visible);void dispatchGetNewSurface();void closeSystemDialogs(String reason);/*** Called for wallpaper windows when their offsets or zoom level change.*/void dispatchWallpaperOffsets(float x, float y, float xStep, float yStep, float zoom, boolean sync);void dispatchWallpaperCommand(String action, int x, int y,int z, in Bundle extras, boolean sync);/*** Drag/drop events*/void dispatchDragEvent(in DragEvent event);/*** Pointer icon events*/void updatePointerIcon(float x, float y);/*** Called for non-application windows when the enter animation has completed.*/void dispatchWindowShown();/*** Called when Keyboard Shortcuts are requested for the window.*/void requestAppKeyboardShortcuts(IResultReceiver receiver, int deviceId);/*** Called when Scroll Capture support is requested for a window.** @param callbacks to receive responses*/void requestScrollCapture(in IScrollCaptureResponseListener callbacks);
}

IWindow是怎么赋值并一步步传入WMS端的呢，由下面代码可以看出，它是在ViewRootImpl中进行赋值的

//定义
​    final W mWindow;
...public ViewRootImpl(@UiContext Context context, Display display, IWindowSession session, WindowLayout windowLayout) {...mWindow = new W(this);... }W如下static class W extends IWindow.Stub {private final WeakReference<ViewRootImpl> mViewAncestor;private final IWindowSession mWindowSession;W(ViewRootImpl viewAncestor) {mViewAncestor = new WeakReference<ViewRootImpl>(viewAncestor);mWindowSession = viewAncestor.mWindowSession;}
...public void setView(View view, WindowManager.LayoutParams attrs, View panelParentView, int userId) {
//此时将mWindow传入，这个方法会一步步调用到Server端WMS中res = mWindowSession.addToDisplayAsUser(mWindow, mWindowAttributes,getHostVisibility(), mDisplay.getDisplayId(), userId,mInsetsController.getRequestedVisibleTypes(), inputChannel, mTempInsets, mTempControls, attachedFrame, compatScale);
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