禁用关闭按钮(关闭变灰)

在窗体类中添加如下代码即可禁用关闭按钮(关闭按钮变灰):
       protected override CreateParams CreateParams
        {
            get
            {
                int CS_NOCLOSE = 0x200;
                CreateParams parameters = base.CreateParams;
                parameters.ClassStyle |= CS_NOCLOSE;
                return parameters;
            }
        }

 

偶不理解其实现原理,懂的朋友请为我讲解一下,谢谢.