VBA：有像抽象类这样的东西吗？

Question

我正在使用一个接口来确保一些类似的类实现一些强制方法（子/函数）。

例子：

• 接口 I1 声明 M1 和 M2 方法
• C1 和 C2 实现 I1，并有自己的 M1 和 M2 版本。

C1 和 C2 也需要完全相同的方法，例如方法 SM1 和 SM2。

为了避免重复 SM1 和 SM2，我想定义一个抽象类 AC：

• 实现 I1
• 定义 SM1 和 SM2。

将由 C1 和 C2 扩展

这个解决方案在 Java 中确实是可能的，但我没有找到在 VBA 中做同样事情的任何文档。 （VB.Net 似乎允许抽象类使用关键字 MustInherit。）

在 VBA 中是否可以确认？

Answer 1

VBA 中没有继承。

您可以定义一个接口，并使用Implements 关键字在类中实现它。但是，如果您希望基类预先实现共享功能，则必须使用复制粘贴方法。

相关阅读：
How to use the Implements in Excel VBA
How to use comparison methods between class object modules in VBA in a similar manner as VB.NET?

Answer 2

您可以在 VBA 中实现半装饰器 :-) 模式。假设我们有一个基类和两个子类。如果在子类中使用 Implements 关键字，您将确保子类具有与基类相同的接口，同时在每个子类中声明基类的私有实例，并将子类的调用重定向到基类。

注意：这里的基类是普通类，你仍然可以创建它的实例（所以它不是真正的抽象类）。

例子：

' Standard module

Sub main()
    Dim a As New ChildA
    Dim b As New ChildB

    a.State = 2
    b.State = 5

    Debug.Print TypeOf a Is Base
    Debug.Print TypeOf b Is Base

    TestPolymorphic a
    TestPolymorphic b
End Sub

Private Sub TestPolymorphic(ByRef obj As Base)
    obj.Polymorphic
End Sub

' -----------------------------------------------

' Base class module

Private m_state As Byte

Public Event StateChanged(oldState As Byte, newState As Byte)

Public Property Get State() As Byte
    State = m_state
End Property

Public Property Let State(ByVal newState As Byte)
    Dim oldState As Byte
    oldState = m_state
    m_state = newState
    RaiseEvent StateChanged(oldState, newState)
End Property

Sub Polymorphic()
    Err.Raise 123, , "Implement in child class"
End Sub

Private Sub Class_Initialize()
    m_state = 1
End Sub

' -----------------------------------------------

' ChildA class module

Implements Base
Private WithEvents m_base As Base

Private Sub Class_Initialize()
    Set m_base = New Base
End Sub

Public Property Get State() As Byte
    State = Base_State
End Property

Public Property Let State(ByVal newState As Byte)
    Base_State = newState
End Property

Public Sub Polymorphic()
    Base_Polymorphic
End Sub

Private Property Get Base_State() As Byte
    Base_State = m_base.State
End Property

Private Property Let Base_State(ByVal newState As Byte)
    m_base.State = newState
End Property

Private Sub Base_Polymorphic()
    Debug.Print "In Child A ..."
End Sub

Private Sub m_base_StateChanged(oldState As Byte, newState As Byte)
    Debug.Print "State of 'Child A' instance has changed from " & oldState & " to " & newState
End Sub

Output:
' State of 'Child A' instance has changed from 1 to 2
' State of 'Child B' instance has changed from 1 to 5
' True
' True
' In Child A ...
' In Child B ...

Answer 3

我对 vba 中抽象类的解决方案： View

'------------------------- 
' Standard module

Sub Main()

    Dim objC1 As C1
    Dim objC2 As C2
    Dim objCollection As New Collection

    Set objC1 = New C1
    Set objC2 = New C2

    With objC1
        .getInterface.M1 "Hello C1!"
        temp1 = .getInterface.M2(objCollection)

        .getSuperClass.SM1 "Hi C1!!!"
        temp3 = .getSuperClass.SM2(objCollection)

    End With

    Debug.Print vbCrLf

    With objC2
        .getInterface.M1 "Hello C2!"
        temp1 = .getInterface.M2(objCollection)

        .getSuperClass.SM1 "Hi C2!!!"
        temp3 = .getSuperClass.SM2(objCollection)

    End With

End Sub


' -----------------------------------------------

' IAbstracat class module

Sub SM1(strString As String): End Sub
Function SM2(varItem As Variant) As String: End Function


' -----------------------------------------------

' Abstracat class module

Implements IAbstract

'Each class must implement these methods, in a particular way
Sub M1(strString As String): End Sub
Function M2(varItem As Variant) As String: End Function


'The sub classes will extend SM1 and SM2
Private Sub IAbstract_SM1(strString As String)
    Debug.Print "Sub IAbstract_SM1: " & strString
End Sub


'The sub classes will extend SM1 and SM2
 Private Function IAbstract_SM2(varItem As Variant) As String

    Dim strMyString As String

    strMyString = "Function IAbstract_SM2 => ObjPtr(varItem): " & ObjPtr(varItem)
    Debug.Print strMyString

    IAbstract_SM2 = strMyString

End Function


' -----------------------------------------------

' C1 class module

Implements Abstract

Private Type TC1
    objConcretSuperClass As Abstract
    objInterfaceSuperClass As IAbstract
    objInterfaceSubClass As Abstract
End Type

Private this As TC1


'if you do not need to initialize anything, then this is it:
Private Sub Class_Initialize()

    With this

        'creating an instance of class' Abstract'
        Set .objConcretSuperClass = New Abstract


        'Referencing the' Abstract 'interface, where are the extended methods
        Set .objInterfaceSuperClass = .objConcretSuperClass


        'Creating a refence for the C1 interface, which is the class' Abstract'
        'Here we have the particular implementations of M1 and M2
        Set .objInterfaceSubClass = Me

    End With

End Sub



'With this we can do:
'   set objC1 = New C1
'   objC1.getInterface.Abstract_M1
'   objC1.getInterface.Abstract_M2
Property Get getInterface() As Abstract
    Set getInterface = this.objInterfaceSubClass
End Property



'With this we can call the methods defined in' Abstract ': SM1 and SM2
'   set objC1 = New C1
'   objC1.getSuperClass.SM1 "hello!"
'   temp = objC1.getSuperClass.SM2 (New Collection)
Property Get getSuperClass() As IAbstract
    Set getSuperClass = this.objInterfaceSuperClass
End Property

'Here we have the particular implementations of M1 and M2
Private Sub Abstract_M1(strString As String)
    Debug.Print "Class C1 => Sub Abstract_M1: " & strString
End Sub

Private Function Abstract_M2(varItem As Variant) As String
    Debug.Print "Class C1 => Function Abstract_M2: " & ObjPtr(varItem)
End Function


' -----------------------------------------------

' C2 class module

Implements Abstract

Private Type TC2
    objConcretSuperClass As Abstract
    objInterfaceSuperClass As IAbstract
    objInterfaceSubClass As Abstract
End Type

Private this As TC2

'if you do not need to initialize anything, then this is it:
Private Sub Class_Initialize()

    With this

        'creating an instance of class' Abstract'
        Set .objConcretSuperClass = New Abstract

        'Referencing the' Abstract 'interface, where are the extended methods
        Set .objInterfaceSuperClass = .objConcretSuperClass

        'Creating a refence for the C1 interface, which is the class' Abstract'
        'Here we have the particular implementations of M1 and M2
        Set .objInterfaceSubClass = Me

    End With

End Sub



'With this we can do:
'   set objC2 = New C2
'   objC2.getInterface.Abstract_M1
'   objC2.getInterface.Abstract_M2
Property Get getInterface() As Abstract
    Set getInterface = this.objInterfaceSubClass
End Property

'With this we can call the methods defined in' Abstract ': SM1 and SM2
'   set objC1 = New C1
'   objC1.getSuperClass.SM1 "hello!"
'   temp = objC1.getSuperClass.SM2 (New Collection)
Property Get getSuperClass() As IAbstract
    Set getSuperClass = this.objInterfaceSuperClass
End Property

'Here we have the particular implementations of M1 and M2
Private Sub Abstract_M1(strString As String)
    Debug.Print "Class C2 => Sub Abstract_M1: " & strString
End Sub

Private Function Abstract_M2(varItem As Variant) As String
    Debug.Print "Class C2 => Function Abstract_M2: " & ObjPtr(varItem)
End Function

立即检查窗口（CTRL + G）：

Class C1 => Sub Abstract_M1: Hello C1!
Class C1 => Function Abstract_M2: 550324728
Sub IAbstract_SM1: Hi C1!!!
Function IAbstract_SM2 => ObjPtr(varItem): 550324728

Class C2 => Sub Abstract_M1: Hello C2!
Class C2 => Function Abstract_M2: 550324728
Sub IAbstract_SM1: Hi C2!!!
Function IAbstract_SM2 => ObjPtr(varItem): 550324728