Building a CheckBoxList Validator Control - Part 2

Source: http://www.dotnetjunkies.com/Tutorial/ECCCD6A6-B312-41CB-87A1-10BB5D641D20.dcik

Part 2 - Part 1 - Building a Custom Validator Control
As promised, this week we will be going over how to add client-side JavaScript to a custom validator control. But last week I was asked a very interesting question. What validator control should I use to validate that a CheckBox was checked within a CheckBoxList? The anwser was simple, NONE. None of the validator controls in the .NET valiator control suite does this type of validation. So, in this article not only are we going to discuss how to add JavaScript validation control for client-side validation, but how to create a CheckBoxListRequiredFieldValidator control. Wow, now that is one hell of a long name, excuse my english! So let's get to it! In the first part of this article I'll go over some of the problems I ran into building this control and how I solved them. Then we'll look at the source code and finally the implementation code.

Creating the CheckBoxListRequiredFieldValidator required a little object manipulation and trickery. Mainly because the CheckBoxList control is not a control that is supported by any of the typical validation control and hence if you try to set any of their ControlToValidate properties to a CheckBoxList an exception would be thrown. Documentation on this subject is nill so I began to experiment. I found that if I override the ControlPropertiesValid base property and return true I could validate any server control I wanted.
The second tricky part was figuring out how client-side validation was done, but this was easily figured out by walking through the WebUIValidation.js and looking at how typical validation controls do it. Well, I always find that looking at code is a lot easier than reading about it so let's look at the code.

RadioButtonListRequiredFieldValidator.cs

using System;
using System.Text;
using System.Web.UI;
using System.Web.UI.WebControls;

namespace Validators {

  public class RadioButtonListRequiredFieldValidator : BaseValidator {


   protected override bool ControlPropertiesValid(){

     return true;

   }


   protected override bool EvaluateIsValid() {

     return this.EvaluateIsChecked();

   }



   protected bool EvaluateIsChecked() {

     CheckBoxList _cbl = ( ( CheckBoxList ) this.FindControl( this . ControlToValidate ) );

     foreach( ListItem li in _cbl.Items ) {

      if ( li.Selected == true ) {

       return true;

      }

     }
      return false;

   }

   protected override void OnPreRender( EventArgs e ){

    if ( this.EnableClientScript ) { this.ClientScript(); }
     base.OnPreRender( e );

   }

   protected void ClientScript() {
    this.Attributes["evaluationfunction"] = "cb_vefify";

    StringBuilder sb_Script = new StringBuilder();
    sb_Script.Append( "<script language=\"javascript\">" );
    sb_Script.Append( "\r" );
    sb_Script.Append( "\r" );
    sb_Script.Append( "function cb_vefify(val) {" );
    sb_Script.Append( "\r" );
    sb_Script.Append( "var val = document.all[document.all[\"" );
    sb_Script.Append( this.ID );
    sb_Script.Append( "\"].controltovalidate];" );
    sb_Script.Append( "\r" );
    sb_Script.Append( "var col = val.all;" );
    sb_Script.Append( "\r" );
    sb_Script.Append( "if ( col != null ) {" );
    sb_Script.Append( "\r" );
    sb_Script.Append( "for ( i = 0; i < col.length; i++ ) {" );
    sb_Script.Append( "\r" );
    sb_Script.Append( "if (col.item(i).tagName == \"INPUT\") {" );
    sb_Script.Append( "\r" );
    sb_Script.Append( "if ( col.item(i).checked ) {" );
    sb_Script.Append( "\r" );
    sb_Script.Append( "\r" );
    sb_Script.Append( "return true;" );
    sb_Script.Append( "\r" );
    sb_Script.Append( "}" );
    sb_Script.Append( "\r" );
    sb_Script.Append( "}" );
    sb_Script.Append( "\r" );
    sb_Script.Append( "}" );
    sb_Script.Append( "\r" );
    sb_Script.Append( "\r" );
    sb_Script.Append( "\r" );
    sb_Script.Append( "return false;" );
    sb_Script.Append( "\r" );
    sb_Script.Append( "}" );
    sb_Script.Append( "\r" );
    sb_Script.Append( "}" );
    sb_Script.Append( "\r" );
    sb_Script.Append( "</script>" );
    this.Page.RegisterClientScriptBlock( "RBLScript", sb_Script.ToString() );
   
   }

  }

}

Compile Code - Make.Bat

csc.exe /target:library /out:../../bin/RadioButtonListRequiredFieldValidator.dll *.cs /r:System.dll,System.Web.dll
pause

Note: Make sure to copy the assembly into your application /bin directory to use.

Web Form - TestValidator.aspx

<%@ Register TagPrefix="DNJValidators" Namespace="Validators" Assembly="RadioButtonListRequiredFieldValidator" %>
<%@ import namespace="System.Data.SqlClient" %>

<script language="C#" runat="Server">



protected void Page_Load( object sender, EventArgs e ){




if ( ! IsPostBack ) this.BindCBL();


}

protected void BindCBL(){

SqlConnection SqlCon = new SqlConnection( "server=localhost;database=northwind;trusted_connection=true" );
SqlCommand SqlCmd = new SqlCommand( "SELECT TOP 10 ProductName, ProductID FROM Products", SqlCon );

SqlCon.Open();
cb.DataSource = SqlCmd.ExecuteReader();
cb.DataTextField = "ProductName";
cb.DataValueField = "ProductID";
cb.DataBind();

}

</script>


<html>
<body>
<form runat="server">

<H3>RadioButtonList Validator</H3>

<!-- Summary -->
<asp:ValidationSummary
id="valSum"
DisplayMode="BulletList"
runat="server"
HeaderText="You must enter a value in the following fields:"
Font-Name="verdana"
Font-Size="8" />
<BR>
<!-- Summary -->

<P>

<!-- Our Validator -->

<B>You must select one item</B>
<DNJValidators:RadioButtonListRequiredFieldValidator
ID="valMessage"
ControlToValidate="cb"
RUNAT="SERVER"
EnableClientScript="true"
ErrorMessage="You must check at least one check box">
*
</DNJValidators:RadioButtonListRequiredFieldValidator>
<BR>
<asp:CheckBoxList runat="server" id="cb" />

<!-- Our Validator -->

<P>

<!-- Intrinsic Validator -->

<B>You must fill out</B>
<asp:RequiredFieldValidator
id="RF"
runat="server"
ControlToValidate="txt"
ErrorMessage="You must fill out text box">
*
</asp:RequiredFieldValidator>
<BR>
<asp:TextBox id="txt" runat="server" />

<!-- Intrinsic Validator -->

<p>

<asp:Button id="submit" Text="Submit" runat="server" />
</form>
</body>
</html>

You have probably noticed three new things in this server control when compared to the last. The first is the ControlPropertiesValid we discussed earlier. Second, is the OnPreRender event and third is the ClientScript method. The following table contains a description of each.