How do I check particular attributes exist or not in XML?

Question

Part of the XML content:

<section name="Header">
  <placeholder name="HeaderPane"></placeholder>
</section>

<section name="Middle" split="20">
  <placeholder name="ContentLeft" ></placeholder>
  <placeholder name="ContentMiddle"></placeholder>
  <placeholder name="ContentRight"></placeholder>
</section>

<section name="Bottom">
  <placeholder name="BottomPane"></placeholder>
</section>

I want to check in each node and if attribute split exist, try to assign an attribute value in a variable.

Inside a loop, I try:

foreach (XmlNode xNode in nodeListName)
{
    if(xNode.ParentNode.Attributes["split"].Value != "")
    {
        parentSplit = xNode.ParentNode.Attributes["split"].Value;
    }
}

But I'm wrong if the condition checks only the value, not the existence of attributes. How should I check for the existence of attributes?

While this might not have been true at the time this question was asked, nowadays there's an [XmlElement.HasAttribute Method](https://learn.microsoft.com/en-us/dotnet/api/system.xml.xmlelement.hasattribute?view=net-5.0) that, to me, seems well suited for such use cases. Just in case someone stumbles upon this... — loptrinho, Jul 28 '21 at 10:59

Paul · Accepted Answer · 2016-04-27T08:52:54.077

54

You can actually index directly into the Attributes collection (if you are using C# not VB):

foreach (XmlNode xNode in nodeListName)
{
  XmlNode parent = xNode.ParentNode;
  if (parent.Attributes != null
     && parent.Attributes["split"] != null)
  {
     parentSplit = parent.Attributes["split"].Value;
  }
}

edited Apr 27 '16 at 08:52

answered Aug 25 '11 at 08:06

Paul

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4

Throws an exception if the node has zero attributes. You need to first test that the Attributes collection is not null. – Ian Thompson Sep 09 '14 at 23:57
2

I guess with new syntactic sugar: `if (parent?.Attributes["split"] != null)` – Arin Taylor Feb 08 '17 at 16:32
I would think more like `if (parent.Attributes?["name"] != null)` – Sam Axe Oct 18 '18 at 07:05

Ben · Answer 2 · 2013-11-10T13:52:39.230

If your code is dealing with XmlElements objects (rather than XmlNodes) then there is the method XmlElement.HasAttribute(string name).

So if you are only looking for attributes on elements (which it looks like from the OP) then it may be more robust to cast as an element, check for null, and then use the HasAttribute method.

foreach (XmlNode xNode in nodeListName)
{
  XmlElement xParentEle = xNode.ParentNode as XmlElement;
  if((xParentEle != null) && xParentEle.HasAttribute("split"))
  {
     parentSplit = xParentEle.Attributes["split"].Value;
  }
}

score 10 · Answer 3 · answered Mar 05 '20 at 13:04

10

Just for the newcomers: the recent versions of C# allows the use of ? operator to check nulls assignments

parentSplit = xNode.ParentNode.Attributes["split"]?.Value;

answered Mar 05 '20 at 13:04

Óscar Alberto Fernández Muñoz

121
1
5

score 7 · Answer 4 · edited Dec 16 '18 at 12:02

7

You can use LINQ to XML,

XDocument doc = XDocument.Load(file);

var result = (from ele in doc.Descendants("section")
              select ele).ToList();

foreach (var t in result)
{
    if (t.Attributes("split").Count() != 0)
    {
        // Exist
    }

    // Suggestion from @UrbanEsc
    if(t.Attributes("split").Any())
    {

    }
}

OR

 XDocument doc = XDocument.Load(file);

 var result = (from ele in doc.Descendants("section").Attributes("split")
               select ele).ToList();

 foreach (var t in result)
 {
     // Response.Write("<br/>" +  t.Value);
 }

edited Dec 16 '18 at 12:02

Peter Mortensen

30,738
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answered Aug 25 '11 at 08:06

KV Prajapati

93,659
19
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186

1

+1 for Linq to XML. Instead of Count() != 0 you could use Any() – Aug 25 '11 at 08:13
@UrbanEsc - just out of curiousity, is there anything gained by using Any() rather than Count()? – Tim Aug 25 '11 at 08:24
Check this SO topic http://stackoverflow.com/questions/305092/which-method-performs-better-any-vs-count-0 – Aug 25 '11 at 08:36

score 5 · Answer 5 · answered Mar 15 '14 at 13:36

5

var splitEle = xn.Attributes["split"];

if (splitEle !=null){
    return splitEle .Value;
}

answered Mar 15 '14 at 13:36

user3423251

51
1
1

Tim · Answer 6 · 2011-08-25T08:17:44.547

3

EDIT

Disregard - you can't use ItemOf (that's what I get for typing before I test). I'd strikethrough the text if I could figure out how...or maybe I'll simply delete the answer, since it was ultimately wrong and useless.

END EDIT

You can use the ItemOf(string) property in the XmlAttributesCollection to see if the attribute exists. It returns null if it's not found.

foreach (XmlNode xNode in nodeListName)
{
    if (xNode.ParentNode.Attributes.ItemOf["split"] != null)
    {
         parentSplit = xNode.ParentNode.Attributes["split"].Value;
    }
}

XmlAttributeCollection.ItemOf Property (String)

edited Aug 25 '11 at 08:17

answered Aug 25 '11 at 07:56

Tim

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i mean check attributes `split` exist. if attributes exist assign attribute value in variable.Thanks. – 4b0 Aug 25 '11 at 08:00
1

@Shree - the code above will check to see if the attribute "split" exists, if it does, if will assign the value of the attribute to `parentSplit`. Note that if you have more than one XmlNode in nodeListName that has a ParentNode with a "split" attribute, the last one in the list will be assigned to parentSplit, overwriting previous ones (if any). – Tim Aug 25 '11 at 08:05
ItemOf actually refers to a direct index into the Attribute collection. – Paul Aug 25 '11 at 08:08
ItemOf is the VB way of interacting with this. Indexing directly into the collection is the C# method. – Paul Aug 25 '11 at 08:16

score 1 · Answer 7 · edited Dec 16 '18 at 12:03

Another way to handle the situation is exception handling.

Every time a non-existent value is called, your code will recover from the exception and just continue with the loop. In the catch-block you can handle the error the same way you write it down in your else-statement when the expression (... != null) returns false. Of course throwing and handling exceptions is a relatively costly operation which might not be ideal depending on the performance requirements.

score 1 · Answer 8 · answered Feb 21 '18 at 20:12

1

You can use the GetNamedItem method to check and see if the attribute is available. If null is returned, then it isn't available. Here is your code with that check in place:

foreach (XmlNode xNode in nodeListName)
{
    if(xNode.ParentNode.Attributes.GetNamedItem("split") != null )
    {
        if(xNode.ParentNode.Attributes["split"].Value != "")
        {
            parentSplit = xNode.ParentNode.Attributes["split"].Value;
        }
    }  
}

answered Feb 21 '18 at 20:12

Rich

11
1

As others here have mentioned, it always good to check if xNode.ParentNode.Attributes is null before continuing. – Rich Feb 23 '18 at 16:26

How do I check particular attributes exist or not in XML?

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