Namespace Undo
    Public Interface ICommand
        ''' <summary>
        ''' 运行一条需要记录在撤销栈的命令
        ''' </summary>
        Sub Execute()


        ''' <summary>
        ''' 重做命令
        ''' </summary>
        Sub Redo()

        ''' <summary>
        ''' 撤销命令
        ''' </summary>
        Sub Undo()
    End Interface
End NameSpace