VBA：子对象属性变更时如何更新父类对应属性值

我正在构建树形结构的任务列表，包含Task_List和Task两个类。Task_List可嵌套其他Task_List或Task，其多项属性为所含子项对应属性的汇总值（如Duration属性为所有子项Duration之和）。

已实现大部分功能（包括子对象访问父类），但难以找到优雅的方式在子对象属性变更时更新Task_List的对应汇总属性。目前尝试的三种方案均存在缺陷：

• 方案1：子对象的X属性变更时，触发父类的公共函数，重置父类X值后遍历所有子项重新求和赋值
  • 问题：实现繁琐，每次变更都需遍历所有子项，数据量大时性能损耗严重
• 方案2：为Task_List添加X属性的Let方法，子对象调用该方法先减去旧值，再加上新值
  • 问题：比方案1高效，但父类属性可被非子对象修改，无法限制调用方
• 方案3：与方案2类似，但传递整个子对象，父类验证该对象是否为自身子项
  • 问题：无法实现，怀疑VBA不支持该方式

寻求相关指导与帮助，可补充更多信息。

简化示例代码 #

Task类模块 #

Private Type Task
   Name As String
   Value As Long
   Parent as Task_List
End Type

Private self As Task 

Public Sub Initialize(Parent as Task_List)
   Set self.Parent = Parent
End Sub

Public Property Get Parent() as Task_List
   Set Parent = Self.Parent
End Property

Property Let Name(ByVal Name As String)
   self.Name = Name   
End Property
 
Property Get Name() As String
   Name = self.Name
End Property

' 这里同时写了方案2和3的调用，实际只会用其中一种
Property Let Value(ByVal Value As Long)

   Call self.Parent.Option_2(-self.Value)
   Call self.Parent.Option_3(self,-1)

   self.Value = Value

   Call self.Parent.Option_3(self,1)
   Call self.Parent.Option_2(self.Value)
 
End Property

Property Get Value() As Long
   Value = self.Value
End Property

Task列表类 #

Private Type Task_List

   Name As String
   SubTasks As New Collection
   Value As Long

End Type

Private self As Task_List

Public Property Get SubTasks() As Collection
   Set SubTasks = self.SubTasks
End Property

Public Property Let SubTasks(SubTask_Coll As Collection)
   Set self.SubTasks = SubTask_Coll
End Property

Property Let Name(ByVal Name As String)
   self.Name = Name
End Property

Property Get Name() As String
   Name = self.Name
End Property

Property Get Value() As Long
   Value = self.Value
End Property

Public Sub Option_2(ByVal Update_Value as long, _
                    Optional ByVal Multiplier as Long = 1)

   self.Value = self.Value + (Multiplier * Update_Value)

End Sub

Public Sub Option_3(ByVal Child_Task as Variant, _
                    Optional ByVal Multiplier as Long = 1)

   On Error Resume Next

      If Child_Task.Parent = self Then
         self.Value = self.Value + (Multiplier * Child_Task.Value)
      End If

   On Error GoTo 0

End Sub

Public Sub Option_1()

   Dim Cur_Sum As Long, Cur_Task as Variant
   For Each Cur_Task In self.SubTasks

      Cur_Sum = Cur_Sum + Cur_Task.Value

   Next Cur_Task
   self.Value = Cur_Sum

End Sub

使用示例 #

Sub Example()

   Dim Main_List As New Task_List
   Main_List.Name = "Bake Bread"

   Dim T1 As New Task
   T1.Initialize Main_List
   Main_List.Subtasks.Add T1

   T1.Name = "Buy Ingredients"
   T1.Value = 250

   Dim T2 As New Task
   T2.Initialize Main_List
   Main_List.Subtasks.Add T2

   T2.Name = "Do Baking"
   T2.Value = 400

   Debug.Print Main_List.SubTasks(1).Name
   Debug.Print Main_List.SubTasks(2).Name

   Debug.Print Main_List.Value
   
End Sub

内容的提问来源于stack exchange，提问作者Steve