excel - 正确编码构造函数

Question

我正在尝试在 VBA excel 中实现模型- View -演示者用户界面。为了做到这一点，我一直在编写不同的模型类。这是一个例子:

Option Explicit

Private Type TModel
    FilterCol As Collection
    N As Integer
End Type

Private this As TModel

Public Property Get FilterCol() As Collection
    Set FilterCol = this.FilterCol
End Property
Public Property Let FilterCol(ByVal value As Collection)
    Set this.FilterCol = value
End Property

Public Property Get N() As Integer
    Set N = this.N
End Property
Public Property Let N(ByVal value As Integer)
    Set this.N = value
End Property

这个名为“FilterModel”的类是 MSFormObject 的集合。为了正确使用该集合，我需要新建它。所以我使用它的代码看起来有点像这样:

Sub testFilter()
Dim Filterm As FilterModel
Dim DefaultFilterLine As New FilterLine

Set Filterm = New FilterModel
Filterm.FilterCol = New Collection

'Set DefaultFilter
Filterm.FilterCol.Add DefaultFilterLine

'DoStuff
With New frmFilter
    Set .Model = Filterm
    .Show
End With
End Sub

如果我在添加某些内容之前不新建属性 FilterCol(在本例中为默认过滤器)，它将不起作用。这是我的问题:

有没有办法覆盖我的新类的新语句，以便让它也更新到 FilterCol 集合中。据我的研究，我现在知道这将被称为构造函数。

但是如何正确实现 VBA 类的构造函数呢？

类似于:

Private Sub Class_Initialize()
Set this.FilterCol = New Collection
N = 0
End Sub

如果我这样做，那么我会在“Property Let N(Byval Value as integer)”行中收到错误。错误消息显示“需要对象”。

Answer 1

这是一个可行的解决方案。我建议使用 F8 逐行浏览代码以了解那里发生了什么。 Debug.print 将值打印到立即窗口中。

这是FilterModel类:

'''   FilterModel class
Option Explicit

Private pFilterCol As Collection
Private pN As Integer

Public Property Get FilterCol() As Collection
    Set FilterCol = pFilterCol
End Property

Public Property Let FilterCol(ByVal value As Collection)
    Set pFilterCol = value
End Property

Public Property Get N() As Integer
    N = pN
End Property

Public Property Let N(ByVal value As Integer)
    pN = value
End Property

Private Sub Class_Initialize()
    Set pFilterCol = New Collection
    pN = 0
End Sub

这是用于测试它的模块代码:

'''   random module
Option Explicit

Sub testFilter()

    Dim Filterm As FilterModel

    Set Filterm = New FilterModel
    Filterm.FilterCol = New Collection

    '''   default values (specified in Class_Initialize())
    Debug.Print Filterm.N
    Debug.Print Filterm.FilterCol.Count

    '''   set the values through Property Let
    Filterm.FilterCol.Add "whatever"
    Filterm.FilterCol.Add "whenever"
    Filterm.N = 6

    '''   print the new values (through Property Get)
    Debug.Print Filterm.N
    Debug.Print Filterm.FilterCol.Count
    Debug.Print Filterm.FilterCol(1)
    Debug.Print Filterm.FilterCol(2)

End Sub