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MatchEvaluator Delegate of a Regular Expression Replace Method in ASP.Net

By Pankaj Lohani on Dec 10, 2013
This article explains the MatchEvaluator Delegate of a custom verification for each match found by a Regular Expression Replace method.


This article explains the MatchEvaluator Delegate. You can use this delegate method to perform a custom verification for each match found by a Regular Expression Replace method. For each matched string, the Replace method calls the MatchEvaluator delegate method with a Match object that represents the match.

System.Text.RegularExpressions Namespace

using System.Text.RegularExpressions;

The System.Text.RegularExpressions namespace contains classes that provide access to the .NET Framework Regular Expression engine. This namespace has the the "Match" class that represents the results from a single Regular Expression match.

MatchEvaluator Delegate

The MatchEvaluator delegate represents the method that is called each time a Regular Expression match is found during a "Replace" method.

return regex.Replace(InputTxt, new MatchEvaluator(MatchRecords));

In a specified input string, replaces all strings that match a specified Regular Expression with a string returned by a MatchEvaluator delegate. The Regex.Replace method processes text replacements. In a Replace method we pass two arguments, the first argument is the input and the second argument is the replacement string.

public string MatchRecords(Match m)


        return ("<span class=highlight>" + m.Value + "</span>");



The "Match" object represents the results from a single Regular Expression match.


FilterExpression Property


The FilterExpression property value is a format string expression or a string processed by the String.Format method and a filtering expression applied when data is retrieved using the Select method.


<asp:SqlDataSource ID="dsDetails" runat="server" ConnectionString="<%$ConnectionStrings:dbconnection %>"

 SelectCommand="select * from EmployeeInformation" FilterExpression="Emp_Name LIKE '%{0}%'">


Now  I will show you how to search the records in a GridView using MatchEvaluator. Let's use the following procedure.

Create DataBase and Table in SQL Server

Create Database Employee

use Employee

create table EmployeeInformation


EmpId int,

Emp_Name varchar(max),

Emp_Address nvarchar(max),

Emp_Department varchar(max)


Write the following procedure to insert the values in the table's columns:

insert into EmployeeInformation values(101,'Pankaj Lohani','A-43 Vinod New Delhi','Web Development')

insert into EmployeeInformation values(102,'Nimit Joshi','B-44 Laxminagar New Delhi','Web Development')

insert into EmployeeInformation values(103,'Pravesh Khanduri','C-45 Pratap Vihar New Delhi','Teacher')

insert into EmployeeInformation values(104,'Amit Senwal','D-46 R.K puram New Delhi','Web Development')

insert into EmployeeInformation values(105,'Ravi Kumar','E-47 Saket New Delhi','Testing')

insert into EmployeeInformation values(106,'Ainul Hasan','F-48 Saraswati Kunj New Delhi','Web Development')

insert into EmployeeInformation values(107,'Ashish','F-49 Vinod Nagar New Delhi','Software Engineer')


Write the following query to execute the table schema:


select * from EmployeeInformation




Step 1:

Open Visual Studio then select "Create New Website" --> ASP.NET Web Site.


Step 2:

Now go to the Solution Explorer to the right side of the application and use the procedure shown in the following figure:


Step 3:

Add a new Web form in the empty web application as in the figure given below.


Step 4:

Write the following code in the GridForm.aspx page:

<%@ Page Language="C#" AutoEventWireup="true" CodeFile="EmployeeDetails.aspx.cs" Inherits="EmployeeDetails" %>


<!DOCTYPE html>


<html xmlns="">

<head id="Head1" runat="server">

<title>Highlight the Search Keywords in Gridview </title>

<style type="text/css">

.GridviewDiv {font-size100%font-family'Lucida Grande''Lucida Sans Unicode'VerdanaArialHeleveticasans-serifcolor#303933;}

Table.Gridview{border:solid 1px #df5015;}

.Gridview th{color:#FFFFFF;border-right-color:#abb079;border-bottom-color:#abb079;padding:0.5em 0.5em 0.5em 0.5em;text-align:center

.Gridview td{border-bottom-color:#f0f2da;border-right-color:#f0f2da;padding:0.5em 0.5em 0.5em 0.5em;}

.Gridview tr{colorBlackbackground-colorWhitetext-align:left}

:link,:visited { color#DF4F13text-decoration:none }

.highlight {text-decorationnone;color:black;background:white;}




<form id="form1" runat="server">

<div class="GridviewDiv">


Enter Employee Name :

<asp:TextBox ID="txtsrchbox" runat="server" />  

<asp:Button ID="btnSearch" Text="Search" runat="server"

Style="top:5pxpositionrelative" OnClick="btnSearch_Click1"/>  

<asp:Button ID="btnClear" runat="server" Text="Clear" Style="top5px;

positionrelative" OnClick="btnClear_Click1"/><br />

<br />


<asp:GridView ID="gvEmpDetails" runat="server" AutoGenerateColumns="False" AllowPaging="True"

AllowSorting="True" DataSourceID="dsDetails" Width="540px" CssClass="Gridview" BackColor="White" 

BorderColor="#E7E7FF" BorderStyle="None" BorderWidth="1px" CellPadding="3" GridLines="Horizontal" >

    <FooterStyle BackColor="#B5C7DE" ForeColor="#4A3C8C" />

<HeaderStyle BackColor="#4A3C8C" Font-Bold="True" ForeColor="#F7F7F7" />

    <AlternatingRowStyle BackColor="#F7F7F7" />


<asp:TemplateField HeaderText="Emp_Id">


<asp:Label ID="lblEmpId" Text='<%# GetRecord(Eval("EmpId").ToString()) %>' runat="server"/>



    <asp:TemplateField HeaderText="Emp_Name">


<asp:Label ID="lblEmpname" Text='<%# GetRecord(Eval("Emp_Name").ToString()) %>' runat="server"/>



<asp:TemplateField HeaderText="Emp_Address">


<asp:Label ID="lblAddress" Text='<%# Eval("Emp_Address"%>' runat="server"/>



<asp:TemplateField HeaderText="Emp_Department">


<asp:Label ID="lblDepartment" Text='<%#Eval("Emp_Department"%>' runat="server"></asp:Label>




    <PagerStyle BackColor="#E7E7FF" ForeColor="#4A3C8C" HorizontalAlign="Right" />

    <RowStyle BackColor="#E7E7FF" ForeColor="#4A3C8C" />

    <SelectedRowStyle BackColor="#738A9C" Font-Bold="True" ForeColor="#F7F7F7" />

    <SortedAscendingCellStyle BackColor="#F4F4FD" />

    <SortedAscendingHeaderStyle BackColor="#5A4C9D" />

    <SortedDescendingCellStyle BackColor="#D8D8F0" />

    <SortedDescendingHeaderStyle BackColor="#3E3277" />



<asp:SqlDataSource ID="dsDetails" runat="server" ConnectionString="<%$ConnectionStrings:dbconnection %>"

 SelectCommand="select * from EmployeeInformation" FilterExpression="Emp_Name LIKE '%{0}%'">


<asp:ControlParameter Name="Emp_Name" ControlID="txtsrchbox" PropertyName="Text" />







Add the connectionstring string to the Web.Config file as in the following:



<add name="dbconnection" connectionString="Data Source=; Initial Catalog=Employee; 

User=; Password=***" providerName="SqlClient"/>



In the preceding EmployeeDetails.aspx page we have the TemplateField consisting of two templates, an ItemTemplate that has a Label whose Text property is set to the value of the Employeename data field, and the data-binding syntax:


<asp:Label ID="lblEmpId" Text='<%# GetRecord(Eval("EmpId").ToString()) %>' runat="server"/>


that indicates that the fieldName data field is bound to the specified Web control property.


Design View of EmployeeDetails.aspx




Now write the following code in EmployeeDetails.aspx.cs:


Step 4 :


using System;

using System.Collections.Generic;

using System.Linq;

using System.Web;

using System.Data;

using System.Data.SqlClient;

using System.Text.RegularExpressions;

using System.Web.UI;

using System.Web.UI.WebControls;


public partial class EmployeeDetails : System.Web.UI.Page


    private string str = "";

    protected void Page_Load(object sender, EventArgs e)




    public string GetRecord(string InputTxt)


        string srch = txtsrchbox.Text;

        Regex regex= new Regex(srch.Replace(" ""|").Trim(), RegexOptions.IgnoreCase);

        return regex.Replace(InputTxt, new MatchEvaluator(MatchRecords));



    public string MatchRecords(Match m)


        return ("<span class=highlight>" + m.Value + "</span>");


    protected void btnSearch_Click1(object sender, EventArgs e)


        str = txtsrchbox.Text;


    protected void btnClear_Click1(object sender, EventArgs e)


        txtsrchbox.Text = "";

        str = "";





Step 5 :

Debug the application by pressing F5 to execute the Web form. After debugging the application the output will be as in the following figure:


Step 6 :

Now write the incomplete name on a given TextBox  then click on the search button as in the figure given below.


Step 7 :

Now search the employee details through the single char of the name and click on the search button as in the figure given below.


Step 8 :

Search the details by the last name of the employee as in the figure given below.