关于vba：使用变量引用集合时”对象无效或不再设置”

“Object Invalid or no Longer Set” when using Variable to Reference Collection

在回答这个问题的过程中，我编写了一个简单的函数来测试MS Access表是否包含提供的数组中的所有字段：

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Function ValidateFields(strTbl As String, arrReq As Variant) As Boolean
Dim fld
Dim fldTmp As Field
On Error GoTo err
For Each fld In arrReq
Set fldTmp = CurrentDb.TableDefs(strTbl).Fields(fld)
Next fld
ValidateFields = True
err:
Exit Function
End Function

1 2	?ValidateFields("TempTable", Array("Field1","Field2","Field3")) False

这按预期执行，但是为了提高效率，我尝试将Fields Collection分配给For Each循环之外的变量：

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Function ValidateFields(strTbl As String, arrReq As Variant) As Boolean
Dim fld
Dim fldTmp As Field
Dim colFld As Fields
Set colFld = CurrentDb.TableDefs(strTbl).Fields
On Error GoTo err
For Each fld In arrReq
Set fldTmp = colFld(fld)
Next fld
ValidateFields = True
err:
Exit Function
End Function

现在，如果我注释掉On Error语句，则会收到以下错误，并突出显示原因行Set fldTmp = colFld(fld)：

Run-time error '3420':
Object invalid or no longer set.

为什么变量colFld在For Each循环中丢失其值？