Checking for null values if element does not exist

Question

I am getting values for a number of elements in a .resx file. On some of the the data elements the <comment> child element does not exist so when I run the following I will get a NullReferenceException.

foreach (var node in XDocument.Load(filePath).DescendantNodes())
{
    var element = node as XElement;

    if (element?.Name == "data")
    {
        values.Add(new ResxString
        {
            LineKey = element.Attribute("name").Value,
            LineValue = element.Value.Trim(),
            LineComment = element.Element("comment").Value  //fails here
        });
    }
}

I have tried the following:

LineComment = element.Element("comment").Value != null ? 
              element.Element("comment").Value : ""

And:

LineComment = element.Element("comment").Value == null ?
              "" : element.Element("comment").Value

However I am still getting an error? Any help appreciated.

Notice -- seems like the problem is you are doing .Value on "null" aka null.Value — Tyler Nichols, Sep 07 '17 at 19:46
What about using the null propagation operator (`?.`), like you did with in your `if` condition... `element.Element("comment")?.Value`. Or just `LineComment = element.Element("comment") == null ? "" : element.Element("comment").Value;` — Rufus L, Sep 07 '17 at 19:54

Salah Akbari · Accepted Answer · 2017-09-11T11:59:31.450

2

Use Null-conditional (?.) Operator:

LineComment = element.Element("comment")?.Value

It used to test for null before performing a member access.

edited Sep 11 '17 at 11:59

answered Sep 07 '17 at 19:45

Salah Akbari

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Erik Philips · Answer 2 · 2017-09-08T01:53:25.623

2

If you're going to use Linq, don't just partially use it: (Just expanding on S. Akbari's Answer)

values = XDocument.Load(filePath)
  .DescendantNodes()
  .Select(dn => dn as XElement)
  .Where(xe => xe?.Name == "data")
  .Select(xe => new new ResxString
  {
         LineKey = element.Attribute("name").Value,
         LineValue = element.Value.Trim(),
         LineComment = element.Element("comment")?.Value 
  })
  .ToList();  // or to array or whatever

edited Sep 08 '17 at 01:53

answered Sep 07 '17 at 19:55

Erik Philips

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2

wouldn't `element` be `xe` in your example? Also, you might want to call out that you're using the null conditional operator, and that is where the problem is – Rufus L Sep 07 '17 at 19:57

score 0 · Answer 3 · answered Sep 07 '17 at 20:08

0

Casting an element or attribute to a nullable type is enough. You'll either get the value or null.

var LineComment = (string)element.Element("comment");

or

var LineKey = (string)element.Attribute("name");

answered Sep 07 '17 at 20:08

L.B

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Checking for null values if element does not exist

3 Answers3

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