Question

The real Author name is : PolarBear.

My function searched PolarBear, the result PolarBear was highlighted as I wished.

I searched Polarbear, polarbear and poLarbear, the PolarBear did appeared in result but was not highlighted as I wished.

How can I make the highlighting case insensitive like the search does? Thank you.

Highlighting Code:

    private void searchComByAuthor()
    {
        // Process the list of files found in the directory. 
        string[] fileEntries = Directory.GetFiles(sourceDirXML);
        foreach (string fileName in fileEntries)
        {
            XmlDocument xmlDoc = new XmlDocument(); //* create an xml document object.

            string docPath = fileName;

            xmlDoc.Load(docPath); //* load the XML document from the specified file.

            XmlNodeList nodeList = xmlDoc.GetElementsByTagName("item");

            foreach (XmlNode node in nodeList)
            {

                XmlElement itemElement = (XmlElement)node;

                string itemAuthor = itemElement.GetElementsByTagName("author")[0].InnerText;

                if (itemAuthor.ToLower() == txtComAuthor.Text.ToString().ToLower())
                {
                    string itemTitle = itemElement.GetElementsByTagName("title")[0].InnerText;
                    string itemDate = itemElement.GetElementsByTagName("pubDate")[0].InnerText;
                    string itemDescription = itemElement.GetElementsByTagName("description")[0].InnerText;
                    string itemXMLFile = Path.GetFileNameWithoutExtension(fileName);

                    richComByTemplate.AppendText("SYMBOL: " + itemXMLFile + "\nAUTHOR: " + itemAuthor + "\nDATE: " + itemDate +
                                                "\nTITLE: " + itemTitle + "\nDESCRIPTION: " + itemDescription + "\n\n--------\n\n");
                }
            }
        }

        int pointer = 0;
        int index = 0;
        string keyword = txtComAuthor.Text;
        string shadow = richComByTemplate.Text;

        while (true)
        {
            //Searching in the copy/shadow
            index = shadow.IndexOf(keyword, pointer);
            //if keyword not found then the loop will break
            if ((index == -1) || (String.IsNullOrEmpty(keyword)))
            {
                break;
            }
            richComByTemplate.Select(index, keyword.Length);
            richComByTemplate.SelectionColor = Color.Red;
            richComByTemplate.SelectionFont = new System.Drawing.Font(richComByTemplate.Font, FontStyle.Bold);
            pointer = index + keyword.Length;
        }

Answer 1

You can try using an overload of the IndexOf method that uses a StringComparison enumeration.

index = shadow.IndexOf(keyword, pointer,StringComparison.InvariantCultureIgnoreCase); 

from second MSDN link:

When you call a string comparison method such as String.Compare, String.Equals, or String.IndexOf, you should always call an overload that includes a parameter of type StringComparison so that you can specify the type of comparison that the method performs. For more information, see Best Practices for Using Strings in the .NET Framework.

small working test example:

public partial class Form1 : Form
{
    public Form1()
    {
        InitializeComponent();
    }

    private void button1_Click(object sender, EventArgs e)
    {
        int pointer = 0;
        int index = 0;
        string keyword = txtComAuthor.Text;
        string shadow = richComByTemplate.Text;

        while (true)
        {
            //Searching in the copy/shadow 
            index = shadow.IndexOf(keyword, pointer, StringComparison.InvariantCultureIgnoreCase);
            //if keyword not found then the loop will break 
            if ((index == -1) || (String.IsNullOrEmpty(keyword)))
            {
                break;
            }
            richComByTemplate.Select(index, keyword.Length);
            richComByTemplate.SelectionColor = Color.Red;
            richComByTemplate.SelectionFont = new System.Drawing.Font(richComByTemplate.Font, FontStyle.Bold);
            pointer = index + keyword.Length;
        } 

    }
}