判断控件是否已经被创建

// Resize the edit control contained in the view to// fill the entire view when the view's window is// resized. CMdiView is a CView derived class.void CMdiView::OnSize(UINT nType, int cx, int cy) {   CView::OnSize(nType, cx, cy);   // Resize edit to fill the whole view.   // OnSize can be called before OnInitialUpdate   // so make sure the edit control has been created.   if (::IsWindow(m_Edit.GetSafeHwnd()))   {      m_Edit.MoveWindow (0, 0, cx, cy);   }}