示例：激活父标签组后读取单个标签的值

本示例阐述了在某个标签所属的 TagGroup 对象设置为“活动”后立即读取标签值的方法。
这将在单个 Tag 对象上执行 RefreshFromSource 方法，无需向 RefreshFromSource 方法传递参数。
Sub TagReadUsingTagRefresh()
  On Error Resume Next
  Dim oGroup As TagGroup
  Dim oTag As Tag
  Dim vValue As Variant
  Err.Clear
  If oGroup Is Nothing Then
    Set oGroup = Application.CreateTagGroup(Me.AreaName, 500)
      If Err.Number Then
        LogDiagnosticsMessage "Error creating TagGroup. Error: " _
          & Err.Description, ftDiagSeverityError
        Exit Sub
      End If
    Set oTag = oGroup.Add("System\Second")
    oGroup.Active = True
    oTag.RefreshFromSource
    vValue = oTag.Value
    Select Case Err.Number
      Case 0:
        MsgBox "System\Second = " & vValue
      Case tagErrorReadValue:
        MsgBox "Error to reading tag value. Error: " & _
        oTag.LastErrorString
      Case tagErrorOperationFailed:
        MsgBox "Failed to read from tag. Error: " & Err.Description
    End Select
  End If
End Sub
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