MDI子窗口始终显示为MDI客户区的子窗口. MDI父级中的深灰色窗口.您无法使用停靠的面板来掩盖它，子窗口将在面板的后面中显示.显然不可见.您必须为客户区域留出空间，这是一项艰巨的要求.

MDI child windows are always shown as a child of the MDI client area. The dark gray window in an MDI parent. You cannot cover this up with a docked panel, the child windows will show behind the panel. Obviously not visible. You must leave room for the client area, a hard requirement.