vb6相当于list<someclass>

在VB 6中没有与泛型直接等效的 List<T> 在vb.net中找到。然而,有这样一件事 Collection 在VB 6中,它提供了类似的功能。主要的区别是一个vb 6 收藏 是 不是强类型 ,这意味着所有对象都存储为 Variants 在集合中。在某些情况下,这是有益的,因为它允许您在同一集合中存储许多不同类型的数据,实际上,VB在内部使用此对象。很容易使用 收藏 以及向上投射对象,因为它们是从类中检索到的,但您几乎无能为力。不能在VB运行时实现强类型集合。

也就是说,有一个变通方案可以实现。与在引入泛型之前如何在vb.net的早期版本中实现集合类似, 你可以把 收藏 在类中,只有 收藏 是通过从此类公开的方法 . 这种设计模式通常被称为 “自定义集合” .

这确实有自动处理强制转换的好处,并且减少了代码的使用者必须记住这样的实现细节。它考虑了(极有可能)在运行时循环通过一个集合的可能性,该集合只包含一种类型的对象,但意外添加了第二种不兼容的对象类型,从而导致代码引发异常。当然,缺点是您必须重新实现 收藏 以自定义集合上的公共方法的形式对自己进行对象化。

下面是一个例子,说明您可能会怎么做:

Public Class CustomerCollection

    ''#Internal collection, exposed by this class
    Private m_Customers As Collection

    Private Sub Class_Initialize()
        ''#Set up the internal collection
        Set m_Customers = New Collection
    End Sub

    Public Sub Add(ByVal cust as Customer, Optional ByVal key as String)
        ''#Add the Customer object to the internal collection
        If IsMissing(key) Then
            m_Customers.Add cust
        Else
            m_Customers.Add cust, key
        End If
    End Sub

    Public Property Get Count() As Integer
        ''#Return the number of objects in the internal collection
        Count = m_Customers.Count
    End Property

    Public Sub Remove(ByVal index As Variant)
        ''#Remove the specified object from the internal collection,
        ''# either by its index or its key
        m_Customers.Remove index
    End Sub

    Public Function Item(ByVal index As Variant) as Customer
        ''#Return the specified object from the internal collection,
        ''# either by its index or its key
        Set Item = m_Customers.Item(index)
    End Function

    Public Sub Clear()
        ''#Removes all objects from the internal collection
        Set m_Customers = New Collection
    End Sub

End Class

请注意,为了设置自定义集合的 Item 属性作为集合的默认方法(如内置 收藏 对象),需要在VB 6 IDE中执行以下步骤:

1. 从“工具”菜单中,单击“过程属性”

2. 从“名称”组合框中选择自定义类的名称。

3. 当对话框出现时,单击“高级”按钮。

4. 在“过程ID”组合框中选择“(默认)”项。

5. 点击“确定”

如果您还希望允许使用 For Each 语法(也像内置的 收藏 对象),可以添加 NewEnum 自定义类的函数:

Public Property Get NewEnum() As IUnknown
    ''#Provides support for enumeration using For Each
    Set NewEnum = m_Customers.[_NewEnum]
End Property

完成后,需要指示vb使用此属性:

1. 如前所述,从“工具”菜单打开“过程属性”对话框。

2. 从“名称”组合框中选择自定义类的名称。

3. 当对话框出现时,单击“高级”按钮。

4. 在“过程ID”组合框中键入数字“-4”。

5. 点击“确定”

这是arraylist的实现。可以将它用作强类型类的基(显然不是通过继承,而是通过codygray答案中表示的组合),但如果不需要类型安全性,它比集合类要好得多。

Option Explicit

Private mavInternalArray() As Variant
Private mlArraySize As Long
Private mlCount As Long
Private mlGrowSize As Long
Private mfZeroIndex As Boolean

'---------------------------------------------------------------------------------------
' Procedure Clear
'---------------------------------------------------------------------------------------
Public Sub Clear()
          Dim index As Long

        For index = 0 To mlCount - 1
            If IsObject(mavInternalArray(index)) Then
                Set mavInternalArray(index) = Nothing
            End If
        Next index
        mlCount = 0

End Sub



'---------------------------------------------------------------------------------------
' Procedure Swap
'---------------------------------------------------------------------------------------
Public Sub Swap(Index1 As Long, index2 As Long)
          Dim vTmp As Variant


        If IsObject(mavInternalArray(index2)) Then
            Set vTmp = mavInternalArray(index2)
        Else
            vTmp = mavInternalArray(index2)
        End If

        If IsObject(mavInternalArray(Index1)) Then
            Set mavInternalArray(index2) = mavInternalArray(Index1)
        Else
           mavInternalArray(index2) = mavInternalArray(Index1)
       End If

       If IsObject(vTmp) Then
           Set mavInternalArray(Index1) = vTmp
       Else
           mavInternalArray(Index1) = vTmp
       End If


End Sub

Public Property Get ZeroIndex() As Boolean
        ZeroIndex = mfZeroIndex
End Property

Public Property Let ZeroIndex(fZeroIndex As Boolean)
        mfZeroIndex = fZeroIndex
End Property

Public Property Get GrowSize() As Long
        GrowSize = mlGrowSize
End Property

Public Property Let GrowSize(lNewSize As Long)
        Debug.Assert lNewSize > 0
        mlGrowSize = lNewSize
End Property

Private Sub Class_Initialize()
        mlGrowSize = 50
        mlArraySize = mlGrowSize
        mfZeroIndex = True
        mlCount = 0


        ReDim mavInternalArray(0 To mlGrowSize - 1)

End Sub

'---------------------------------------------------------------------------------------
' Procedure Remove
'---------------------------------------------------------------------------------------
Public Sub Remove(index As Long)
        Dim index2 As Long


        For index2 = index To mlCount - 2
            If IsObject(mavInternalArray(index2 + 1)) Then
                Set mavInternalArray(index2) = mavInternalArray(index2 + 1)
            Else
                mavInternalArray(index2) = mavInternalArray(index2 + 1)
            End If
        Next index2
          If mlCount <= 0 Then
            Exit Sub
          End If
        mlCount = mlCount - 1
        If IsObject(mavInternalArray(mlCount)) Then
           Set mavInternalArray(mlCount) = Nothing
       Else
           mavInternalArray(mlCount) = False
       End If
End Sub

'---------------------------------------------------------------------------------------
' Procedure Items
'---------------------------------------------------------------------------------------
Public Function Items(index As Long) As Variant
        If Not mfZeroIndex Then
            index = index - 1
        End If

        If index < mlCount And index >= 0 Then
            If IsObject(mavInternalArray(index)) Then
                Set Items = mavInternalArray(index)
            Else
                Items = mavInternalArray(index)
            End If
       End If
End Function

Public Sub SetItem(index As Long, Item As Variant)
        If Not mfZeroIndex Then
            index = index - 1
        End If
        If IsObject(Item) Then
            Set mavInternalArray(index) = Item
        Else
            mavInternalArray(index) = Item
        End If
End Sub

'---------------------------------------------------------------------------------------
' Procedure Add
'---------------------------------------------------------------------------------------
Public Function Add(vItem As Variant) As Long

        mlCount = mlCount + 1
        If mlCount > mlArraySize Then
            mlArraySize = mlArraySize + mlGrowSize
            ReDim Preserve mavInternalArray(0 To mlArraySize - 1)
        End If

        If IsObject(vItem) Then
            Set mavInternalArray(mlCount - 1) = vItem
        Else
            mavInternalArray(mlCount - 1) = vItem
       End If

       Add = mlCount - 1

End Function

'---------------------------------------------------------------------------------------
' Procedure ItemArray
'---------------------------------------------------------------------------------------
Public Function ItemArray() As Variant
        Dim vReturnArray As Variant

        vReturnArray = mavInternalArray
        ReDim Preserve vReturnArray(0 To mlCount - 1)
        ItemArray = vReturnArray
End Function

Public Function Count() As Long
        Count = mlCount
End Function


'---------------------------------------------------------------------------------------
' Procedure Insert
'---------------------------------------------------------------------------------------
Public Function Insert(index As Long, vItem As Variant) As Long
        Dim index2 As Long

        'Make sure array is large enough for a new item
        mlCount = mlCount + 1
        If mlCount > mlArraySize Then
            mlArraySize = mlArraySize + mlGrowSize
            ReDim Preserve mavInternalArray(0 To mlArraySize - 1)
        End If

        'Bump all the items with a higher index up one spot

        If index >= mlCount - 1 Then
            If IsObject(vItem) Then
                Set mavInternalArray(mlCount - 1) = vItem
            Else
               mavInternalArray(mlCount - 1) = vItem
           End If
       Else

           For index2 = mlCount - 1 To index + 1 Step -1
               If IsObject(vItem) Then
                   Set mavInternalArray(index2) = mavInternalArray(index2 - 1)
               Else
                   mavInternalArray(index2) = mavInternalArray(index2 - 1)
               End If
           Next index2

           If IsObject(vItem) Then
               Set mavInternalArray(index) = vItem
           Else
               mavInternalArray(index) = vItem
           End If
       End If
       Insert = mlCount - 1

End Function


Public Sub Clone(ByRef cDestinationDynamicArray As clsDynamicArray)
        Dim index As Long

        If cDestinationDynamicArray Is Nothing Then
            Set cDestinationDynamicArray = New clsDynamicArray
        End If

        cDestinationDynamicArray.Clear

        For index = 0 To mlCount - 1
            Call cDestinationDynamicArray.Add(mavInternalArray(index))
        Next index

End Sub

Public Property Get NewEnum() As IUnknown
    ''#Provides support for enumeration using For Each
    Set NewEnum = m_Customers.[_NewEnum]
End Property

编辑:如果Cody Gray的解决方案对您的需求来说太过庞大,您可以尝试“穷人列表”解决方案,如下所示:

 Dim l() as somefixedclass
 Redim l(0)

 '...
 'increase size dynamically:
 Redim Preserve l(ubound(l)+1)
 '...

当然,A List<somefixedclass> (C)或A List(Of somefixedclass) 在vb.net中更“用户友好”,因为它有查找、删除、添加范围和其他一些有用的方法。旧的vb6结构处理“空列表”情况非常糟糕。别忘了,对于大列表(大小为1000),List<..>Increasement的性能要好得多。

vb6是一种古老的语言。它不包含现代语言(C++、C语言、Java)中的模板类型。因此,您必须将对象作为变量存储在集合中,然后在稍后将其转换回对象类型。