Linq to XML检查空结果 [英] Linq to XML check for null results

问题描述

如果xml文件中存在数据，则以下代码有效.但是，它们不存在datafield.tag.value("90")的时间.如何检查空结果.
例子

The following code works if data exist in the xml file. However, their times when datafield.tag.value("90") doesn’t exist. How can I check for null results.
example

if Num090 = Null then
Num090 = empty string

感谢你的帮助.

Appreciate your help.

Dim xd As XElement = XElement.Load(strFilename)
Dim strPipe As String = Chr(124)
Dim strSpace As String = Chr(10)
Dim strFinalString As String = ""
Dim Records = (From datafields In xd.Descendants("record") Select datafields)
For Each ser As XElement In Records
     Try
           Dim Num090 = (From datafield In ser.Descendants("datafield") Where (datafield.Attribute("tag").Value = "090")
           Select datafield.Elements.ElementAt(0))

           Dim DTIC856 = (From datafield In ser.Descendants("datafield") Where (datafield.Attribute("tag").Value = "856")
           Select datafield).Skip(1).First()
              

     Catch ex As Exception

     Finally

     End Try

Next

推荐答案

可以使用String.IsNullOrEmpty(String)吗?

或者，您可以使用Is Nothing进行检查，如:

Can you use String.IsNullOrEmpty(String)?

Or, you could use Is Nothing to check, as in:

If Num90 Is Nothing Then
  Num90=String.Empty
End If

为什么要为先前分配为XElement的var重新分配给string，如果它为null?

如果将Num090设置为值后想要对Num090做任何事情，我将声明移到Try块之外，并在Finally块中进行后期处理.

Why do you want to reassign a var that was previously assigned as a XElement to a string if it''s null?

If there''s anything you want to do to Num090 after setting it to a value, I''d move the declaration outside the Try block, and do your post processing in the Finally block.

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