上一篇文章讲到了Client端窗口添加流程，本文接着上文往下讲，讲一下Server端的窗口添加流程。

1. WindowManagerService#grantInputChannel

        由grantInputChannel我们可以看到，Client端传入了session对象， 发起者Uid-callingUid，发起者pid-callingPid, 要显示屏幕的displayId, 要显示的图层surface，用于返回到客户端窗口，让WMS使用它来通知客户端的IWindow对象window,窗口的flags, 窗口的privateFlags，窗口的inputFeatures以及窗口类型，windowToken，以及InputChannel，用户应用端和WMS端双方互相通信的通路已经铺好了。

    /**
将 InputChannel 分配给 SurfaceControl，并将其配置为根据其屏幕上的几何图形接收触摸输入。
由 WindowlessWindowManager 用于启用 SurfaceControl 嵌入视图的输入。*/void grantInputChannel(Session session, int callingUid, int callingPid,int displayId, SurfaceControl surface, IWindow window, IBinder hostInputToken,int flags, int privateFlags, int inputFeatures, int type, IBinder windowToken,IBinder focusGrantToken, String inputHandleName, InputChannel outInputChannel) {final int sanitizedType = sanitizeWindowType(session, displayId, windowToken, type);final InputApplicationHandle applicationHandle;final String name;final InputChannel clientChannel;synchronized (mGlobalLock) {
//EmbeddedWindowController是用于跟踪嵌入式窗口。
// 如果嵌入的窗口没有收到输入，则窗口管理器不会跟踪它。但是，如果他们确实收到输入，我们会跟踪调用 PID 以归咎于正确的应用和主机窗口以发送 pointerDownOutsideFocus。EmbeddedWindowController.EmbeddedWindow win =new EmbeddedWindowController.EmbeddedWindow(session, this, window,mInputToWindowMap.get(hostInputToken), callingUid, callingPid,sanitizedType, displayId, focusGrantToken, inputHandleName,(flags & FLAG_NOT_FOCUSABLE) == 0);
//client输入通道确认clientChannel = win.openInputChannel();
//增加一个新的嵌入窗口mEmbeddedWindowController.add(clientChannel.getToken(), win);applicationHandle = win.getApplicationHandle();name = win.toString();}
//updateInputChannelupdateInputChannel(clientChannel.getToken(), callingUid, callingPid, displayId, surface, name, applicationHandle, flags, privateFlags, inputFeatures, sanitizedType, null /* region */, window);clientChannel.copyTo(outInputChannel);}

这里有个很重要的IWindow，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res = mWindowSession.addToDisplayAsUser(mWindow, mWindowAttributes,getHostVisibility(), mDisplay.getDisplayId(), userId,mInsetsController.getRequestedVisibleTypes(), inputChannel, mTempInsets, mTempControls, attachedFrame, compatScale);
​