null reference exception in the code

Question

I am getting NullReferenceException error on "_attr.Append(xmlNode.Attributes["name"]);".

namespace SMAS
{
class Profiles
{
    private XmlTextReader _profReader;
    private XmlDocument _profDoc;

    private const string Url = "http://localhost/teamprofiles.xml";
    private const string XPath = "/teams/team-profile";

    public XmlNodeList Teams{ get; private set; }
    private XmlAttributeCollection _attr;

    public ArrayList Team { get; private set; }

    public void GetTeams()
    {
        _profReader = new XmlTextReader(Url);
        _profDoc = new XmlDocument();

        _profDoc.Load(_profReader);
        Teams = _profDoc.SelectNodes(XPath);

        foreach (XmlNode xmlNode in Teams)
        {
            _attr.Append(xmlNode.Attributes["name"]);
        }
    }
}
}

the teamprofiles.xml file looks like

  <teams>
    <team-profile name="Australia">
      <stats type="Test">
        <span>1877-2010</span>
        <matches>721</matches>
        <won>339</won>
        <lost>186</lost>
        <tied>2</tied>
        <draw>194</draw>
        <percentage>47.01</percentage>
      </stats>
      <stats type="Twenty20">
        <span>2005-2010</span>
        <matches>32</matches>
        <won>18</won>
        <lost>12</lost>
        <tied>1</tied>
        <draw>1</draw>
        <percentage>59.67</percentage>
      </stats>
    </team-profile>
    <team-profile name="Bangladesh">
      <stats type="Test">
        <span>2000-2010</span>
        <matches>66</matches>
        <won>3</won>
        <lost>57</lost>
        <tied>0</tied>
        <draw>6</draw>
        <percentage>4.54</percentage>
      </stats>
    </team-profile>
 </teams>

I am trying to extract names of all teams in an ArrayList. Then i'll extract all stats of all teams and display them in my application. Can you please help me about that null reference exception?

Two tips to avoid NullReferenceException: 1) always initialize fields; 2) avoid using null. — R. Martinho Fernandes
– R. Martinho Fernandes, Commented May 18, 2010 at 16:59
To solve, i did what ReSharper told me to do foreach (XmlNode xmlNode in Teams) { _attr.Append(xmlNode.Attributes["name"]); } I added a null check for Teams before foreach loop. — SMUsamaShah
– SMUsamaShah, Commented May 19, 2010 at 10:55

Pharabus · Accepted Answer · 2010-05-16 14:52:40Z

3

I cant see where you initialise private XmlAttributeCollection _attr;

you can try

 _profDoc.Load(_profReader);
_attr =  _profDoc.DocumentElement.Attributes;

edited May 16, 2010 at 14:52

answered May 16, 2010 at 14:23

Pharabus

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1 Comment

SMUsamaShah Over a year ago

How should i initialize it? i can not initialize it as private XmlAttributeCollection _attr = new XmlAttributeCollection()

Pharabus · Accepted Answer · 2010-05-16 14:51:43Z

3

You never initialize _attr. It's a null reference.

edited May 16, 2010 at 14:51

Pharabus

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answered May 16, 2010 at 14:24

Marcelo Cantos

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2 Comments

SMUsamaShah Over a year ago

With what value should i initialize it?

Pharabus Over a year ago

apologies, i accidently edited this answer rather than my own

R. Martinho Fernandes · Accepted Answer · 2010-05-16 15:05:58Z

1

As others have said, you have to initialize _attr.

With what value?

A XmlAttributeCollection is returned by XmlElement.Attributes. If what you want is the attributes of an element, you can just use that property. If what you want is a "collection of XmlAttribute" but not forcibly a XmlAttributeCollection, you can declare it like this:

ICollection<XmlAttribute> _attr = new List<XmlAttribute>();

And then use ICollection<T>.Add instead of Append.

Or, use LINQ:

_attr = (from node in Teams
        select node.Attributes["name"]).ToList();

answered May 16, 2010 at 15:05

R. Martinho Fernandes

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Comments

Joren · Accepted Answer · 2010-05-16 14:23:48Z

0

It doesn't seem like you ever assign anything to _attr, so of course it'll be null.

answered May 16, 2010 at 14:23

Joren

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