How Do I Solve Object Reference Not Set To An Instance Of An Object

Question

Am trying to loop through xmlnodes. but getting this error "Object reference not set to an instance of an object." My main goal was to loop it through the datgridviewcell but i don't know how i can take it further. I know the column indexes for font,date and comment from my grid. how can i loop through those column indexes and be able to parse the value to string?

 <?xml version="1.0" encoding="utf-8"?>
 <root>
<data name="Button"xml:space="preserve">
<value></value>
<comment>[Font][/Font][DateStamp][/DateStamp[Comment][/Comment]</comment>
 </data>

     XmlNodeList _Nodelist = _doc.SelectNodes("/root");
            foreach(XmlNode _Xnode in _Nodelist)
            {
                XmlNode _data = _Xnode.SelectSingleNode("data");
                XmlNodeList _CommentNodes = _data.SelectNodes("comment");
                if(_CommentNodes != null)
                {
                    foreach(XmlNode node in _CommentNodes)
                    {
                        XmlNode _comment = node.SelectSingleNode("comment");
                        {

                                string _font = _comment["Font"].InnerText; //it throws the error here
                                string _Date = _comment["DateStamp"].InnerText;
                                string _Comment = _comment["Comment"].InnerText;
                        }
                    }
                }
            }

Not sure what the square brackets are for, but [/DateStamp is missing a closing one... — komodosp, Feb 25 '15 at 10:53
possible duplicate of [What is a NullReferenceException and how do I fix it?](http://stackoverflow.com/questions/4660142/what-is-a-nullreferenceexception-and-how-do-i-fix-it) — Ant P, Feb 25 '15 at 14:10

score 0 · Answer 1 · answered Feb 25 '15 at 13:59

Your problems are that

There is only one level of <comment> node, but you are looking for nested comment nodes.
The text inside the <comment> node isn't XML - it's just text content. Thus it cannot be parsed as if it contained child XML elements.

Instead you need to do something like the following:

        XmlNodeList _Nodelist = _doc.SelectNodes("/root");
        foreach (XmlNode root in _Nodelist)
        {
            XmlNode _data = root.SelectSingleNode("data");
            if (_data == null)
                continue;
            XmlNodeList _CommentNodes = _data.SelectNodes("comment");
            foreach (XmlNode _comment in _CommentNodes)
            {
                var text = _comment.InnerText;
                // text = "[Font][/Font][DateStamp][/DateStamp[Comment][/Comment]"
                string _font = text.Between("[Font]", "[/Font]", StringComparison.Ordinal);
                string _Date = text.Between("[DateStamp]", "[/DateStamp]", StringComparison.Ordinal);
                string _Comment = text.Between("[Comment]", "[/Comment]", StringComparison.Ordinal);
            }
        }

Using the extension method:

public static class TextHelper
{
    public static string Between(this string input, string start, string end, StringComparison comparison)
    {
        var startIndex = input.IndexOf(start, comparison);
        if (startIndex < 0)
            return null;
        startIndex += start.Length;
        var endIndex = input.IndexOf(end, startIndex, comparison);
        if (endIndex < 0)
            return null;
        return input.Substring(startIndex, endIndex - startIndex);
    }
}

Note that _Date will be null because, as @colmde noted, "[/DateStamp" is missing a closing bracket.

How Do I Solve Object Reference Not Set To An Instance Of An Object

1 Answers1