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实现一个单元格类,该类具有可以是不同类型的值属性

vb.net

Andrew · 技术社区 · 16 年前

我正在尝试设计一个包含行和单元格的表类型结构。我希望单元类具有值属性。我正在努力研究如何创建一个可以返回一些已定义的不同类型的值,例如integer、single、date、string。我希望单元格值是强类型的,但我不确定如何最好地实现这一点。

到目前为止,我在代码方面的想法是:

Public Class Cell
  Private _value as object
  Public Property Value as Object    // How can I define this so that it return a Type 
    Get                              // e.g. integer, string, etc
      Return _value 
    End Get
    Set(ByVal value as object)
      _value = value
    End Set
End Class

Public Class Row
  Dim _Cells as New List(Of Cell)
  Public Function AddCell(ByVal c as Cell) as Cell
     _Cells.Add(c)
     Return _Cells(_Cells.count - 1)
  End Function

1 回复 | 直到 16 年前

Kamarey 16 年前

这里有一个简单的解决方案,使用基本继承,甚至不使用泛型。我们的想法是,对于所有单元格,都有一个单独的父类。每个列类型都有不同的单元类。这样可以声明行对象中的单元格列表。由于一行中可能有不同的单元格类型,因此不能将它(单元格列表)声明为某些特定单元格类型的列表。但在这种情况下,您可以使用单元格的父类。简而言之,以下是示例:

Public Class Cell
End Class

Public Class Cell_Id
    Inherits Cell
    Public Value As Integer
End Class

Public Class Cell_Name
    Inherits Cell
    Public Value As String
End Class

Public Class Cell_MonthlyTax
    Inherits Cell
    Public Value As Double
End Class


Public Class Row
    Public Cells As New List(Of Cell)

    Public Sub AddCell(ByVal cell As Cell)
        Cells.Add(cell)
    End Sub
End Class


Module Module1

    Sub Main()
        Dim row1 As New Row()
        row1.AddCell(New Cell_Id() With {.Value = 1})
        row1.AddCell(New Cell_Name() With {.Value = "Name1"})
        row1.AddCell(New Cell_MonthlyTax() With {.Value = 12.2})
        Dim row2 As New Row()
        row2.AddCell(New Cell_Id() With {.Value = 2})
        row2.AddCell(New Cell_Name() With {.Value = "Name2"})
        row2.AddCell(New Cell_MonthlyTax() With {.Value = 47.9})
        Dim row3 As New Row()
        row3.AddCell(New Cell_Id() With {.Value = 3})
        row3.AddCell(New Cell_Name() With {.Value = "Name3"})
        row3.AddCell(New Cell_MonthlyTax() With {.Value = 73.3})

        Dim rows As New List(Of Row)(New Row() {row1, row2, row3})

        ' here you loop through rows, in each row select Cell at index 2, cast it down to a specific
        ' type (yes, you should tell to a compiler that you sure that Cell at index 2 is of Cell_MonthlyTax type)
        ' After casting you will get intellisence and see that Value is of Double type.
        ' In cellsOfColumn2 you will get an array of Double (this is not exactly array, but it doesn't matter in our case)
        Dim cellsOfColumn2 = From row In rows Select DirectCast(row.Cells(2), Cell_MonthlyTax).Value

        ' here you may work with array of values as you want, say calculate avarange value
        Dim result = cellsOfColumn2.Average()
    End Sub

End Module