VBA 将 parent class 传递给 child class

Question

我在 SO 上找到了一个很棒的 post，这似乎正是我想要的：Is it possible to access a parent property from a child that is in a collection? 但是我对它的改编给了我 Object doesn't support this property or method.

感谢 Mat's Mug 和 Tomalak，我的代码现在可以运行了：

Parent Class - clsComputer

Option Explicit
Private pCD As clsCD

''''''''''''''''''''''''''''''
' CD property
''''''''''''''''''''''''''''''
Public Property Get CD() As clsCD
    If pCD Is Nothing Then
        Set pCD = New clsCD
        'Per Mat's Mug post, drop the parenthesis
        pCD.Initialze Me
    End If
    Set CD = pCD
End Property
Public Property Set CD(value As clsCD)
    pCD = value
End Property

Child class - clsCD

Option Explicit

Private pParent As clsComputer

'''''''''''''''''''''''''''''
' Status property - READ ONLY
'''''''''''''''''''''''''''''
Public Property Get Status(Optional strHost As String) As String
    Dim strResult As String

    If strHost = "" Then strHost = Me.Parent.HostName

    strResult = RunCMD("cmd /c ""winrs -r:" & strHost & _
        " reg query hklm\system\currentcontrolset\services\cdrom /v start""")
    If InStr(1, strResult, "0x4", vbTextCompare) Then
        Status = "Disabled"
    Else
        Status = "Enabled"
    End If
End Property

'''''''''''''''''''''''''
' Parent property
'''''''''''''''''''''''''
Public Property Get Parent() As clsComputer
    Set Parent = pParent
End Property

'Because as Tomalak points out, you use Set with Objects.
Public Property Set Parent(Obj As clsComputer)
    Set pParent = Obj
End Property

'''''''''''''''''''''''''
' Initialize Method
'''''''''''''''''''''''''
Public Sub Initialize(Obj As clsComputer)
    Set Me.Parent = Obj
End Sub

代码模块 - Module1

Sub test()
    Dim oPC As clsComputer
    Set oPC = New clsComputer
    Debug.Print "CD Status: " & oPC.CD.Status
End Sub

如果我测试 Me，它是一个 object（例如，If IsObject(Me) Then Stop 评估为真），并且当我键入 Me. The Locals 时，Intellisense 会显示 clsComputer 中的所有属性和方法windows 将我显示为 clsComputer object。我知道要检查的所有内容都说我是 clsComputer object，那么我做错了什么？

Answer 1

Public Property Set Parent(ByRef Obj As clsComputer)
    Set pParent = Obj
End Property

Answer 2

我不在电脑旁，所以只是盲目编码

为您的 clsComputer class

试试这个

Option Explicit
Private pCD As clsCD

''''''''''''''''''''''''''''''
' CD property
'''''''''''''''''''''''''''''' 
Public Property Get CD() As clsCD
    Set CD = pCD
End Property

Public Property Set CD(value As clsCD)
    pCD = value
End Property

Sub Class_Initialize()
    Set pCD = New clsCD
    pCD.Initialize(Me)
End Property

Answer 3

经典。

pCD.Initialize (Me) 'Error occurs on this line when using F8

去掉括号。

pCD.Initialize Me

完成。

参数周围的圆括号 强制它被求值并通过 ByVal（不管过程的签名说什么）——并且因为你可能还没有为 clsComputer 定义一个默认的属性然后评估爆炸并且运行时甚至没有到达 Initialize 方法。

也就是说，按值传递对象引用没有错。事实上，这就是 C# 和 VB.NET 默认执行的操作 - 考虑传递 any 参数 ByVal.

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