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

Introduction

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

TalbeSchema

Step 1

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

CreateNewWebsite

Step 2

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

AddNewItem

Step 3

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

AddNewWebForm

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="http://www.w3.org/1999/xhtml">
<head id="Head1" runat="server">
<title>Highlight the Search Keywords in Gridview </title>
<style type="text/css">
.GridviewDiv {font-size: 100%; font-family: 'Lucida Grande', 'Lucida Sans Unicode', Verdana, Arial, Helevetica, sans-serif; color: #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{color: Black; background-color: White; text-align:left}
:link,:visited { color: #DF4F13; text-decoration:none }
.highlight {text-decoration: none;color:black;background:white;}
</style>
</head>
<body>
<form id="form1" runat="server">
<div class="GridviewDiv">
<p>
Enter Employee Name :
<asp:TextBox ID="txtsrchbox" runat="server" />
<asp:Button ID="btnSearch" Text="Search" runat="server"
Style="top:5px; position: relative" OnClick="btnSearch_Click1"/>
<asp:Button ID="btnClear" runat="server" Text="Clear" Style="top: 5px;position: relative" OnClick="btnClear_Click1"/><br />
<br />
</p>
<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" />
<Columns>
<asp:TemplateField HeaderText="Emp_Id">
<ItemTemplate>
<asp:Label ID="lblEmpId" Text='<%# GetRecord(Eval("EmpId").ToString()) %>' runat="server"/>
</ItemTemplate>
</asp:TemplateField>
<asp:TemplateField HeaderText="Emp_Name">
<ItemTemplate>
<asp:Label ID="lblEmpname" Text='<%# GetRecord(Eval("Emp_Name").ToString()) %>' runat="server"/>
</ItemTemplate>
</asp:TemplateField>
<asp:TemplateField HeaderText="Emp_Address">
<ItemTemplate>
<asp:Label ID="lblAddress" Text='<%# Eval("Emp_Address") %>' runat="server"/>
</ItemTemplate>
</asp:TemplateField>
<asp:TemplateField HeaderText="Emp_Department">
<ItemTemplate>
<asp:Label ID="lblDepartment" Text='<%#Eval("Emp_Department") %>' runat="server"></asp:Label>
</ItemTemplate>
</asp:TemplateField>
</Columns>
<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:GridView>
</div>
<asp:SqlDataSource ID="dsDetails" runat="server" ConnectionString="<%$ConnectionStrings:dbconnection %>"
SelectCommand="select * from EmployeeInformation" FilterExpression="Emp_Name LIKE '%{0}%'">
<FilterParameters>
<asp:ControlParameter Name="Emp_Name" ControlID="txtsrchbox" PropertyName="Text" />
</FilterParameters>
</asp:SqlDataSource>
</form>
</body>
</html>

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

<connectionStrings>
<add name="dbconnection" connectionString="Data Source=; Initial Catalog=Employee;
User=; Password=***" providerName="SqlClient"/>
</connectionStrings>

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 5

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 = "";
gvEmpDetails.DataBind();
}
}

Step 6

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

AfterDebug

Step 7

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

SearchEmployee1

Step 8

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

SeachwithSinglechar

Step 9

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

SearchingwithLastName