确定对象是否是VBA中集合的成员

Question

如何确定对象是否是VBA中集合的成员？

具体来说,我需要找出表定义是否是TableDefs集合的成员.

Answer 1

不够好吗？

Public Function Contains(col As Collection, key As Variant) As Boolean
Dim obj As Variant
On Error GoTo err
    Contains = True
    obj = col(key)
    Exit Function
err:

    Contains = False
End Function

Answer 2

不完全优雅,但我能找到的最好(也是最快)的解决方案是使用OnError.对于任何中型到大型集合,这将明显快于迭代.

Public Function InCollection(col As Collection, key As String) As Boolean
  Dim var As Variant
  Dim errNumber As Long

  InCollection = False
  Set var = Nothing

  Err.Clear
  On Error Resume Next
    var = col.Item(key)
    errNumber = CLng(Err.Number)
  On Error GoTo 0

  '5 is not in, 0 and 438 represent incollection
  If errNumber = 5 Then ' it is 5 if not in collection
    InCollection = False
  Else
    InCollection = True
  End If

End Function

Answer 3

您最好的选择是迭代集合的成员,看看是否匹配您正在寻找的东西.相信我,我必须多次这样做.

第二个解决方案(更糟糕的是)捕获"Item not in collection"错误,然后设置一个标志,表示该项目不存在.

Answer 4

这是一个老问题.我仔细阅读了所有答案和评论,测试了性能解决方案.

我想出了我的环境中最快的选项,当集合包含对象和基元时,它不会失败.

Public Function ExistsInCollection(col As Collection, key As Variant) As Boolean
    On Error GoTo err
    ExistsInCollection = True
    IsObject(col.item(key))
    Exit Function
err:
    ExistsInCollection = False
End Function

此外,该解决方案不依赖于硬编码的错误值.因此参数col As Collection可以被其他一些集合类型变量替换,并且该函数仍然可以工作.例如,在我目前的项目中,我会将其作为col As ListColumns.