Selecting XML nodes with same name but different attribute inner text in C#

Question

<item> 
    <title>Aerie Peak</title> 
    <link>http://www.wow-europe.com/realmstatus/index.html#Aerie Peak</link> 
    <description>Aerie Peak - Realm Down - Lang en - Type PvE</description> 
    <category domain="status">Realm Down</category> 
    <category domain="language">en</category> 
    <category domain="type">PvE</category> 

    <category domain="queue">false</category> 
    <guid isPermaLink='false'>EU5-REALM15</guid> 
</item>

I need to select title and status. Here's what I came up with:

string uri = "http://www.wow-europe.com/realmstatus/index.xml"; 
XmlDocument doc = new XmlDocument();  
doc.Load(uri);

XmlNodeList nodes = doc.SelectNodes("//item");

foreach (XmlNode node in nodes)
{
   {
   RealmList.Text += node["title"].InnerText + " - " + 
       node.SelectNodes("category[@domain='status']")[0].InnerText;
   }
}

That gives System.NullReferenceException: Object reference not set to an instance of an object. at the selection line, though. I'm not sure how would I go about selecting the node.

Answer 1

Your code works fine for your example, but the file http://www.wow-europe.com/realmstatus/index.xml contains at least one item element at the time of writing that does not contain a category element.

Because that node is not present, you get the exception.

I'm talking about this XML at the top of http://www.wow-europe.com/realmstatus/index.xml.

<item>
            <title>Alert</title>
            <link>http://www.wow-europe.com/realmstatus/index.html</link>
            <description><p><u><strong>Extended Maintenance 07/07</strong></u></p><p>We will be performing extended maintenance on the realms listed below on Wednesday, July 7th, beginning at 00:01 CEST. The maintenance is scheduled for 24 hours as we prepare for the upcoming expansion. These realms will be playable again at approximately 23:59 on Wednesday, July 7th.</p><p>All realms not listed below will undergo scheduled maintenance beginning at 05:00 CEST and will be available for play at approximately 11:00 CEST. </p><p>Additionally, paid character transfer will be unavailable for the duration of the maintenance.</p><p>[11:10] The maintenance has been extended for all realms. We apologise for any inconvenience this may cause and thank you for your patience while this is being resolved. </p><p>Balnazzar<br />Bloodfeather<br />Darksorrow<br />Defias Brotherhood<br />Earthen Ring<br />Frostwhisper<br />Genjuros<br />Haomarush<br />Hellscream<br />Laughing Skull<br />Lightning's Blade<br />Magtheridon<br />Neptulon<br />Nordrassil<br />Quel'Thalas<br />Ragnaros<br />Ravencrest<br />Runetotem<br />Shadowsong<br />Shattered Hand<br />Silvermoon<br />Skullcrusher<br />Spinebreaker<br />Stormrage<br />Stormreaver<br />Stormscale<br />Sylvanas<br />Terenas<br />The Maelstrom<br />The Venture Co.<br />Thunderhorn</p></description>
            <guid isPermaLink='false'>Alert</guid>

        </item>

I think that's where your problem is.

Answer 2

You have to initialize RealmList and 'Text' member in RealmList too, as string default is null.