Question

At the following code i use foreach loop to check each node in nodelist and remove some of them.
after i remove one node the foreach loop throw the following error:
“The element list has changed. The enumeration operation failed to continue”.
How can i avoid it?

public static XmlNodeList Scan(XmlNodeList nodeList)
        {
            string elementValue = null;
            foreach (XmlNode xmlElement in nodeList)
            {
                elementValue = xmlElement.InnerText;
                if (elementValue.Length >= 6 && elementValue.Substring(0, 3) == "999")
                {
                    continue;
                }
                else 
                {
                    XmlNode node = xmlElement.ParentNode;
                    node.RemoveChild(xmlElement);
                }
            }

            return nodeList;
        }

Answer 1

As you’re not simply removing items from the collection you’re looping over, I’m not sure if “use a for loop” will work.

The following takes two steps:

1. Create a regular list of all the elements you want to detach from their parents.
2. Detatch those elements from their parents – by iterating over the regular list, which isn’t affected by the detachings.

public static XmlNodeList Scan(XmlNodeList nodeList)
{
    List<XmlNode> toRemove = new List<XmlNode>();

    foreach (XmlNode xmlElement in nodeList)
    {
        string elementValue = xmlElement.InnerText;
        if (elementValue.Length < 6 || elementValue.Substring(0, 3) != "999")
        {
            toRemove.Add(xmlElement);
        }
    }

    foreach(XmlNode xmlElement in toRemove)
    {
        XmlNode node = xmlElement.ParentNode;
        node.RemoveChild(xmlElement);
    }

    return nodeList;
}