VBA - 安全地存儲可變引用

Question

我熟悉通過引用將參數傳遞給過程。或者，ParamArray也允許我通過引用將0個或更多參數傳遞給過程的靈活性。但是，這種方法讓我懷疑是否有辦法保留對一個或多個超出程序範圍的變量的引用。我希望第一一線希望是VBA Array功能，當我看到它聲明如下：

Array(ParamArray ArgList() As Variant)

所以，我總結了以下的測試代碼：

Private Sub Test() 

    Dim a As Object 
    Dim b() As Variant 

    ParamArrayTest a 
    Debug.Print TypeName(a) ' Output is 'Dictionary' 
    b = Array(a)   ' b should be like ParamArray ArgList() 
    Set b(0) = Nothing  ' This should clear a 
    Debug.Print TypeName(a) ' Output is still 'Dictionary' 

End Sub 

Private Sub ParamArrayTest(ParamArray ArgList() As Variant) 

    Set ArgList(0) = CreateObject("Scripting.Dictionary") 

End Sub 

不幸的是，這並沒有按我的預期工作。儘管通過ParamArray將參數傳遞到Array函數中，但看起來返回的數組是通過值而不是通過引用。

進一步的研究使我無證VBA /StrPtr/ObjPtr功能。我發現了很多與API RtlMoveMemory函數配合使用的例子。然而，我所閱讀的所有文章強烈建議不要使用這種方法，因爲它很容易使應用程序崩潰。我的一些測試確實使Access崩潰。

另一個想法我是要看看我能一個變量的引用直接分配到另一個：

Private Sub Test() 

    Dim a As Object 
    Dim b As Variant 

    b = ByRef a ' Throws a compiler error 

End Sub 

我只想說，編譯器根本不會允許。我的問題是，變量引用是否可以安全地存儲/保存在一個過程的範圍之外（最好在另一個變量中）？

編輯

我決定這將是更有益的，如果我揭示什麼，我試圖建立一些輕。

我目前正在創建一個包裝類，它將所有的表單/控制事件傳遞給我的模塊之一的過程。它將與2種具有相同控制結構但連接到不同源表的表單一起使用。請記住，代碼是不完整的，但應該足以說明我試圖克服的問題。另外，Database是我的VBA項目名稱。

有四個部分的代碼：

1. Form_TEST_FORM - 表格模塊

   Private Sub Form_Open(Cancel As Integer) 
   
       FormHub.InitForm Me, Cancel 
   
   End Sub 
   

2. FormHub - 模塊

   Public Sub InitForm(_ 
       ByRef Form As Access.Form, _ 
       ByRef Cancel As Integer _ 
   ) 
   
       Dim Evt As Database.EventHandler 
   
       Set Evt = New Database.EventHandler 
       Evt.InitFormObject Form, Cancel 
       FormList.Add Evt, Form.Name 
   
   End Sub 
   
   Private Function FormList() As VBA.Collection 
   
       Static Init As Boolean 
       Static Coll As VBA.Collection 
   
       If Not Init Then 
   
        Set Coll = New VBA.Collection 
        Init = True 
   
       End If 
   
       Set FormList = Coll 
   
   End Function 
   

3. FormControl - 類模塊

   Public Ptr  As Variant ' Pointer to form control variable 
   Public acType As Access.AcControlType 
   

4. EventHandler - 類模塊

   Private WithEvents Form  As Access.Form 
   Private WithEvents SForm As Access.SubForm 
   Private CtrlList   As VBA.Collection 
   
   Private Sub Class_Initialize() 
   
       InitCtrlList 
   
   End Sub 
   
   Public Sub InitFormObject(FormObj As Access.Form, ByRef Cancel As Integer) 
   
       Dim ErrFlag As Boolean 
       Dim Ctrl As Access.Control 
       Dim FCtrl As Database.FormControl 
   
       On Error GoTo Proc_Err 
   
       Set Form = FormObj 
   
       If Form.Controls.Count <> CtrlList.Count Then 
   
        Err.Raise 1, , _ 
        "Form has incorrect number of controls" 
   
       End If 
   
       ' This is where I want to validate the form controls 
       ' and also initialize my event variables. 
       For Each Ctrl In Form.Controls 
   
        If Not CtrlExists(FCtrl, Ctrl.Name) Then 
   
         Err.Raise 2, , _ 
         "Invalid control name" 
   
        ElseIf FCtrl.acType <> Ctrl.ControlType Then 
   
         Err.Raise 3, , _ 
         "Invalid control type" 
   
        Else 
   
         ' Initialize the correct variable with it's 
         ' pointer. This is the part I haven't been 
         ' able to figure out yet. 
         Set FCtrl.Ptr = Ctrl 
   
        End If 
   
       Next 
   
   Proc_End: 
   
       On Error Resume Next 
   
       If ErrFlag Then 
   
        ClearEventVariables 
   
       End If 
   
       Set Ctrl = Nothing 
       Set FCtrl = Nothing 
   
       Exit Sub 
   
   Proc_Err: 
   
       ErrFlag = True 
       Debug.Print "InitFormObject " & _ 
       "Error " & Err & ": " & Err.Description 
       Resume Proc_End 
   
   End Sub 
   
   Private Function CtrlExists(_ 
       ByRef FCtrl As Database.FormControl, _ 
       ByRef CtrlName As String _ 
   ) As Boolean 
   
       On Error Resume Next 
   
       Set FCtrl = CtrlList(CtrlName) 
       CtrlExists = Err = 0 
   
   End Function 
   
   Private Sub InitCtrlList() 
   
       Set CtrlList = New VBA.Collection 
       CtrlList.Add SetCtrlData(SForm, acSubform), "SForm" 
   
   End Sub 
   
   Private Function SetCtrlData(_ 
       ByRef Ctrl As Access.Control, _ 
       ByRef acType As Access.AcControlType _ 
   ) As Database.FormControl 
   
       Set SetCtrlData = New Database.FormControl 
   
       With SetCtrlData 
   
        ' This assignment is where I need to keep a reference 
        ' to the variable in the class. However, it doesn't 
        ' work. 
        Set .Ptr = Ctrl 
        .acType = acType 
   
       End With 
   
   End Function 
   
   Private Sub ClearEventVariables() 
   
       Dim FormCtrl As Database.FormControl 
   
       Set Form = Nothing 
   
       For Each FormCtrl In CtrlList 
   
        ' Assuming I was able to retain a reference to the 
        ' class variable, this would clear it. 
        Set FormCtrl.Ptr = Nothing 
   
       Next 
   
   End Sub 
   
   Private Sub Class_Terminate() 
   
       ClearEventVariables 
       Set CtrlList = Nothing 
   
   End Sub 
   

我只用1個控制在爲了簡單起見，代碼示例。但是，這個想法是爲了在表單設計更改時簡化爲了添加/刪除控件而需要修改多少代碼。或者，如果我必須添加更多表單到項目中。

Answer 1

如果您只需要在單一模塊中引用，聲明爲公共模塊頭。如果你想在任何模塊中引用，在通用模塊頭中聲明爲全局。即使數組和記錄集和連接對象也可以這樣聲明。請注意，如果代碼在運行時中斷，這些變量將丟失它們的值。

或可考慮TempVar的對象變量。如果代碼中斷，它們不會丟失值。但只能存儲數字或文本值，而不能存儲對象。