VBA将父级传递到子级 [英] VBA pass parent class to child class

问题描述

我在SO上找到了一篇不错的帖子，似乎正是我想要的:

I found a great post on SO that seems to be exactly what I want: Is it possible to access a parent property from a child that is in a collection? However my adaptation of it is giving me Object doesn't support this property or method.

我的代码现在可以工作了，这要感谢Mat's Mug和Tomalak:

My code which now works thanks to Mat's Mug and Tomalak:

父类-clsComputer

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

子类-clsCD

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

Code Module - Module1

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

如果我测试我，它是一个对象(例如，如果IsObject(Me)然后Stop 计算为true)，并且当我键入 Me时，Intellisense将显示clsComputer中的所有属性和方法.本地"窗口将我显示为clsComputer对象.我知道要检查的所有内容都说我是一个clsComputer对象，所以我在做什么错了?

If I test Me, it is an object (eg, If IsObject(Me) Then Stop evaluates true), and Intellisense shows all the properties and methods in clsComputer when I type Me. The Locals windows shows Me as a clsComputer object. Everything I know to check says Me is a clsComputer object, so what am I doing wrong?

推荐答案

经典.

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

删除括号.

pCD.Initialize Me

完成.

围绕参数进行强制解析，强制对其进行评估并传递ByVal (无论过程签名怎么说)-而且由于您可能尚未定义默认属性对于 clsComputer ，则评估会崩溃，并且运行时甚至无法使用 Initialize 方法.

Parentheses around a parameter force it to be evaluated and passed ByVal (regardless of what the procedure's signature says) - and since you probably haven't defined a default property for clsComputer then the evaluation blows up and the runtime doesn't even get to the Initialize method.

也就是说，按值传递对象引用没有错.实际上，这就是C#和VB.NET的默认设置-考虑传递 any 参数 ByVal .

That said, there's nothing wrong with passing object reference by value. In fact, that's what C# and VB.NET do by default - consider passing any parameter ByVal.

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