客户端访问服务端的Session。ViewRoot.java

public static IWindowSession getWindowSession(Looper mainLooper) {
        synchronized (mStaticInit) {
            if (!mInitialized) {
                try {
                    InputMethodManager imm = InputMethodManager.getInstance(mainLooper);
                    sWindowSession = IWindowManager.Stub.asInterface(
                            ServiceManager.getService("window"))
                            .openSession(imm.getClient(), imm.getInputContext());
                    mInitialized = true;
                } catch (RemoteException e) {
                }
            }
            return sWindowSession;
        }
    }

客户端和服务端建立联系：setView

                requestLayout();
                try {
                    res = sWindowSession.add(mWindow, mWindowAttributes,
                            getHostVisibility(), mAttachInfo.mContentInsets);
                } catch (RemoteException e) {
                    mAdded = false;
                    mView = null;
                    mAttachInfo.mRootView = null;
                    unscheduleTraversals();
                    throw new RuntimeException("Adding window failed", e);
                } finally {
                    if (restore) {
                        attrs.restore();
                    }
                }