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); }}