CODEWITHSUNDEEP
c#xml
X3074861X
X3074861X

Reputation: 3819

XML - Check for existence of a specific node

I don't know why I'm having so much trouble with this, but I'm hoping someone can get me pointed in the right direction.

I have these few lines of code :

var xDoc = new XmlDocument();
xDoc.LoadXml(xelementVar.ToString());

if (xDoc.ChildNodes[0].HasChildNodes)
{
    for (int i = 0; i < xDoc.ChildNodes[0].ChildNodes.Count; i++)
    {
        var sFormatId = xDoc.ChildNodes[0].ChildNodes[i].Attributes["formatID"].Value;
        // Do some stuff
    }    
// Do some more stuff
}

The problem is that the xDoc I'm getting doesn't always have the formatID node, so I end up getting a null reference exception, although 99% of the time it works perfectly fine.

My question :

How can I check if the formatID node exists before I try to read the Value out of it?

Upvotes: 2

Views: 14632

Answers (6)

Sanjeev Singh
Sanjeev Singh

Reputation: 4076

In most case we face issues because an XPath does not exists, It returns null and our code breaks because of the InnerText.

You can only check XPath exists or not and it returns null when does not exist.

if(XMLDoc.SelectSingleNode("XPath") <> null)
  ErrorCode = XMLDoc.SelectSingleNode("XPath").InnerText

Upvotes: 1

JLRishe
JLRishe

Reputation: 101758

I think a cleaner way to do this would be:

var xDoc = new XmlDocument();
xDoc.LoadXml(xelementVar.ToString());

foreach(XmlNode formatId in xDoc.SelectNodes("/*/*/@formatID"))
{
    string formatIdVal = formatId.Value; // guaranteed to be non-null
    // do stuff with formatIdVal
}

Upvotes: 1

terrybozzio
terrybozzio

Reputation: 4530

You can also do this:

            if (xDoc.ChildNodes[0].HasChildNodes)
            {   
                foreach (XmlNode item in xDoc.ChildNodes[0].ChildNodes)
                {
                    string sFormatId;
                    if(item.Attributes["formatID"] != null)
                       sFormatId = item.Attributes["formatID"].Value;

                    // Do some stuff
                }     
            }

Upvotes: 2

DGibbs
DGibbs

Reputation: 14618

Could you use DefaultIfEmpty()?

E.g

var sFormatId = xDoc.ChildNodes[0].ChildNodes[i].Attributes["formatID"]
                                  .Value.DefaultIfEmpty("not found").Single();

Or as others have suggested, check that the attribute is not null:

if (xDoc.ChildNodes[0].ChildNodes[i].Attributes["formatID"] != null)

Upvotes: 2

Ehsan
Ehsan

Reputation: 32721

you can check that like this

 if(null != xDoc.ChildNodes[0].ChildNode[i].Attributes["formatID"])

Upvotes: 1

sora0419
sora0419

Reputation: 2378

if a node does not exist, it returns null.

if (xDoc.ChildNodes[0].ChildNode[i].Attributes["formatID"] != null)
    sFormatId = xDoc.ChildNodes[0].ChildNodes[i].Attributes["formatID"].Value;

of you can do it a shortcut way

var sFormatId = xDoc.ChildNodes[0].ChildNodes[i].Attributes["formatID"] != null ? xDoc.ChildNodes[0].ChildNodes[i].Attributes["formatID"].Value : "formatID not exist";

The format is like this.

var variable = condition ? A : B;

this is basically saying that if the condition is true, then variable = A, otherwise, variable = B.

Upvotes: 2

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