Wrap tag around searched words in string and Highlight using C# and VB.Net in ASP.Net

Hi nauna,

Check this example. Now please take its reference and correct your code.

HTML

<asp:TextBox runat="server" ID="txtSearch" Text="paragraph one" />
<asp:Button Text="Highlight" runat="server" OnClick="OnHighlight" />

Namespaces

C#

using System.Linq;
using System.Text.RegularExpressions;

VB.Net

Imports System.Linq
Imports System.Text.RegularExpressions

Code

C#

public string HighlightKeyWords(string text, string keywords, string cssClass, bool fullMatch)
{
    if (text == String.Empty || keywords == String.Empty || cssClass == String.Empty)
        return text;
    var words = keywords.Split(new[] { ',' }, StringSplitOptions.RemoveEmptyEntries);
    if (!fullMatch)
    {
        return words.Select(word => word.Trim()).Aggregate(text,
                        (current, pattern) =>
                        Regex.Replace(current, pattern,
                                        string.Format("<div><span style=\"background-color:{0}\">{1}</span></div>", cssClass, "$0"),
                                        RegexOptions.IgnoreCase));
    }
    else
    {
        return words.Select(word => "\\b" + word.Trim() + "\\b")
                    .Aggregate(text, (current, pattern) =>
                                Regex.Replace(current, pattern,
                                string.Format("<div><span style=\"background-color:{0}\">{1}</span><div>", cssClass, "$0"),
                                RegexOptions.IgnoreCase));
    }
}

protected void OnHighlight(object sender, EventArgs e)
{
    string val = "This is paragraph one topic one to add the custom tags.";
    Response.Write(HighlightKeyWords(val, txtSearch.Text.Trim(), "yellow", true));
}

VB.Net

Public Function HighlightKeyWords(ByVal text As String, ByVal keywords As String, ByVal cssClass As String, ByVal fullMatch As Boolean) As String
    If text = String.Empty OrElse keywords = String.Empty OrElse cssClass = String.Empty Then Return text
    Dim words = keywords.Split({","c}, StringSplitOptions.RemoveEmptyEntries)

    If Not fullMatch Then
        Return words.Select(Function(word) word.Trim()) _
        .Aggregate(text, Function(current, pattern) _
                                Regex.Replace(current, pattern,
                                            String.Format("<div><span style=""background-color:{0}"">{1}</span></div>", cssClass, "$0"),
                                            RegexOptions.IgnoreCase))
    Else
        Return words.Select(Function(word) "\b" & word.Trim() & "\b") _
        .Aggregate(text, Function(current, pattern) _
                                Regex.Replace(current, pattern,
                                            String.Format("<div><span style=""background-color:{0}"">{1}</span><div>", cssClass, "$0"),
                                            RegexOptions.IgnoreCase))
    End If
End Function

Protected Sub OnHighlight(ByVal sender As Object, ByVal e As EventArgs)
    Dim val As String = "This is paragraph one topic one to add the custom tags."
    Response.Write(HighlightKeyWords(val, txtSearch.Text.Trim(), "yellow", True))
End Sub

Screenshot