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Question

我熟悉通过引用将参数传递给过程。或者，ParamArray允许我灵活地通过引用将0或更多参数传递给过程。但是，这种方法让我想知道是否有办法保留对程序范围之外的一个或多个变量的引用。当我看到VBA Array函数被声明为这样时，我的第一个希望就是：{/ p>

Array(ParamArray ArgList() As Variant)

所以，我把以下测试代码放在一起：

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，这并没有像我预期的那样奏效。尽管通过Array将参数传递给ParamArray函数，但看起来返回的数组是按值而不是通过引用。

进一步的研究使我了解了未记录的VBA VarPtr / StrPtr / ObjPtr函数。我发现了许多将它们与API RtlMoveMemory函数结合使用的示例。但是，我读到的所有文章都强烈反对使用该方法，因为它很容易使应用程序崩溃。我的一些测试确实让Access崩溃了。

我的另一个想法是看我是否可以直接将一个变量的引用分配给另一个变量：

Private Sub Test()

    Dim a As Object
    Dim b As Variant

    b = ByRef a ' Throws a compiler error

End Sub

只需说，编译器根本不允许这样做。那么我的问题是，可以安全地存储/保存变量引用超出过程的范围（最好是在另一个变量中）吗？

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如果我对我正在努力建立的内容有所了解，我认为会更有帮助。

我目前正在创建一个包装类，它将所有表单/控件事件传递给我的一个模块中的过程。它将与2个具有相同控制结构但连接到不同源表的表单一起使用。请记住，代码不完整，但应足以说明我想要克服的问题。此外，Database是我的VBA项目名称。

代码有四个部分：

Form_TEST_FORM - 表单模块

Private Sub Form_Open(Cancel As Integer)

    FormHub.InitForm Me, Cancel

End Sub

FormHub - 模块

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

FormControl - 课程模块

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

EventHandler - 课程模块

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

为简单起见，我在代码示例中仅使用了1个控件。但是，我的想法是简化我需要修改的代码，以便在表单设计更改时添加/删除控件。或者，如果我必须在项目中添加更多表单。

Answer 1

如果只需要在单个模块中引用，请在模块头中声明为Public。如果要在任何模块中引用，请在通用模块头中声明为Global。甚至可以通过这种方式声明数组和记录集以及连接对象。请注意，如果代码在运行时中断，这些变量将丢失其值。

或者查看TempVar对象变量。如果代码中断，它们不会丢失值。但只能存储数字或文本值，而不能存储对象。

VBA - 安全存储变量引用

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1 个答案: