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Creating Your Own Validation Control In Asp.Net

Validations in a web application is an important aspect of programming because it restricts the user from misusing the system and gives an assurance of a robust system. In ASP.NET Microsoft has provided certain validation controls from which a web developer can apply validations in an easy and less error prone manner.

But sometimes situations are so different that the Microsoft made validation controls are not sufficient to deal with it. Fortunately .net has provided a facility for the developers so that they can create their own validation controls according to their programming needs.

In this tutorial we will discuss the steps for creating a validation control.

Prerequisite

Before you read this tutorial you must assure that you have

hands on experience in creating an ASP.NET web application.
Basic knowledge of validation controls in ASP.NET.

Steps For The Creation Of Validation Control

For creating the validation controls you must follow the steps given below :-

Create a new class and inherit the class from BaseValidator class.
Override the method EvaluateIsValid and write validation logic inside it.
Write properties if required.

These steps becomes more clear when we will work on an example.

Scenario

Consider an scenario in which you are working on a job portal and you are allowing the user to select the primary skills from left listbox and add it on the right listbox. The condition is use can enter maximum 5 skills.

For that we will first create a class called MaxItemsValidator and inherit the class with BaseValidator class as I have mentioned in step 1

public class MaxItemsValidator: BaseValidator {
  public MaxItemsValidator() {

}
}

As you are inheriting the class BaseValidator so you have to override the method EvaluateIsValid. As I have mentioned earlier this is the method where we will write the validation logic.

public class MaxItemsValidator: BaseValidator {
  public MaxItemsValidator() {

}
  protected override bool EvaluateIsValid() {}
}

If you are familiar with custom validator then you must have seen the property args.IsValid. If the value of the property is false then it means that validation fails and if the value is true then it means field is validated. In the similar way if the method EvaluateIsValid() returns false then it means that the validation fails and if true then it means that field is validated.

As I have stated earlier that this validation control will check if the number of items in the listbox is more than 5 then it should give error message and validation should fail. For that we will create a property called MaximumSize which the programmer can set based on the scenario.

public int MaximumSize {
  get;
  set;
}

Now let us write some logic in the EvaluateIsValid() method.

protected override bool EvaluateIsValid() {
  ListBox lb = (ListBox) this.FindControl(ControlToValidate);
  bool status = true;
  if (lb.Items.Count > MaximumSize) {
    status = false;
  }
  return status;
}

In line 1 I am finding the control and then cast it into a local variable lb.

In line 2 I am creating a local variable and initialize it with true.

In line 3 I am check if the number of items in listbox is greater than maximum limit.

In line 5 I am setting the value of status as false. It means that validation fails.

In line 7 I am returning the status.

Now we are done with the validation control. Now it is the time to use this control in ASP.NET web form.

First of all use the register directive for the validation control.

<%@ Register Namespace="MyValidators" TagPrefix="val" %>

Now add the controls on the page.

<asp:ListBox runat="server" ID="lstLeftSide" 
SelectionMode="Multiple">
	<asp:ListItem>Skill 1</asp:ListItem>
	<asp:ListItem>Skill 2</asp:ListItem>
	<asp:ListItem>Skill 3</asp:ListItem>
	<asp:ListItem>Skill 4</asp:ListItem>
	<asp:ListItem>Skill 5</asp:ListItem>
	<asp:ListItem>Skill 6</asp:ListItem>
	<asp:ListItem>Skill 7</asp:ListItem>
	<asp:ListItem>Skill 8</asp:ListItem>
</asp:ListBox>
<asp:Button ID="btnTransferToRight" runat="server" Text=">>" 
onclick="btnTransferToRight_Click" />
<asp:Button ID="btnTransferToLeft" runat="server" Text="<<" 
onclick="btnTransferToLeft_Click" />
	<asp:ListBox runat="server" ID="lstRightSide" 
	SelectionMode="Multiple"></asp:ListBox>
	<asp:Button runat="server" Text="Trigger" ID="btnTrigger" 
onclick=" btnTrigger _Click" />
	<val:MaxItemsValidator runat="server" ControlToValidate="lstRightSide" ErrorMessage="Max limit exceeded" MaximumSize="5"></val:MaxItemsValidator>

Here the first list box i.e. lstLeftSide is the left hand side listbox which contains all the skills. Second list box i.e. lstRightSide is the right hand side listbox where skills will be added.

There are 2 buttons i.e. btnTransferToRight and btnTransferToRight the first one is to move the skills from left hand side listbox to right hand side listbox and the second one will move the skills from right hand side to left hand side listbox.

There is a button called btnTrigger which is for some database operations. And finally we have validation control. In the validation control we have ControlToValidate property- which specifies which control needs to be validated

ErrorMessage- message when the validation fails.

MaximumSize- property defined in the validation controls to specify the maximum number of elements in the listbox.

Note – Here I am not writing the logic for the button clicks because it is not in the scope of this article.

Now we have done with the coding part now it is a time to browse the application

Picture showing the output of creating your first validation control in asp.net

Click to Enlarge

Here I have transferred 6 skills. Now when I click on Trigger an error message will be prompted.

Validation Control Code

using System.Web.UI.WebControls;

namespace MyValidators {
  /// <summary>
  /// Summary description for MaxItemsValidator
  /// </summary>
  public class MaxItemsValidator: BaseValidator {
    public MaxItemsValidator() {
      //
      // TODO: Add constructor logic here
      //
    }

    protected override bool EvaluateIsValid() {
      ListBox lb = (ListBox) this.FindControl(ControlToValidate);
      bool status = true;
      if (lb.Items.Count > MaximumSize) {
        status = false;
      }
      return status;
    }

    public int MaximumSize {
      get;
      set;
    }
  }
}

Web Form ASPX Code

<%@ Page Language="C#" AutoEventWireup="true" CodeFile="NewValidatorConsumer.aspx.cs" Inherits="NewValidatorConsumer" %><%@ Register Namespace="MyValidators" TagPrefix="val" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html
	xmlns="http://www.w3.org/1999/xhtml">
	<head runat="server">
		<title></title>
	</head>
	<body>
		<form id="form1" runat="server">
			<div>
				<asp:ListBox runat="server" ID="lstLeftSide" SelectionMode="Multiple">
					<asp:ListItem>Skill 1</asp:ListItem>
					<asp:ListItem>Skill 2</asp:ListItem>
					<asp:ListItem>Skill 3</asp:ListItem>
					<asp:ListItem>Skill 4</asp:ListItem>
					<asp:ListItem>Skill 5</asp:ListItem>
					<asp:ListItem>Skill 6</asp:ListItem>
					<asp:ListItem>Skill 7</asp:ListItem>
					<asp:ListItem>Skill 8</asp:ListItem>
				</asp:ListBox>
				<asp:Button ID="btnTransferToRight" runat="server" Text=" >>" 
            onclick="btnTransferToRight_Click" />
				<asp:Button ID="btnTransferToLeft" runat="server" Text=" <
					<" 
            onclick="btnTransferToLeft_Click" />
					<asp:ListBox runat="server" ID="lstRightSide" SelectionMode="Multiple"></asp:ListBox>
					<asp:Button runat="server" Text="Trigger" ID="btnTrigger" onclick="btnTrigger_Click" />
					<val:MaxItemsValidator runat="server" ControlToValidate="lstRightSide" ErrorMessage="Max limit exceeded" MaximumSize="5"></val:MaxItemsValidator>
				</div>
			</form>
		</body>
	</html>

Code Behind

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;

public partial class NewValidatorConsumer: System.Web.UI.Page {

  protected void btnTrigger_Click(object sender, EventArgs e) {

}
  protected void btnTransferToRight_Click(object sender, EventArgs e) {
    if (lstLeftSide.SelectedIndex > -1) {
      lstRightSide.Items.Add(lstLeftSide.Items[lstLeftSide.SelectedIndex]);
      lstLeftSide.Items.Remove(lstLeftSide.Items[lstLeftSide.SelectedIndex]);
    }
  }
  protected void btnTransferToLeft_Click(object sender, EventArgs e) {
    if (lstRightSide.SelectedIndex > -1) {
      lstLeftSide.Items.Add(lstRightSide.Items[lstRightSide.SelectedIndex]);
      lstRightSide.Items.Remove(lstRightSide.Items[lstRightSide.SelectedIndex]);
    }
  }
}

Posted By -	Karan Gupta

Posted On -	Friday, October 14, 2011

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