Multiple Fields Validator - An ASP.NET Validation Control

• Download source code - 4.5 KB
• Download demo project - 5.8 KB

Introduction

In an ideal world, web users don't need to authenticate because they are trustworthy, no try-catch because there wouldn't be any bug or unexpected behavior, and you wouldn't be using web validators because users will be submitting valid entries. But since we are not living in that world, I hope we would some time, you might find this validator useful, so bear with me.

Developing with ASP.NET, I've encountered many cases when you only need one field to be filled out of many given fields. To validate in such cases, I used to have a custom validator, or a client-script, or sometimes did server-side validation only.

The problem with a custom validator, and all other ASP.NET validators, is that they are mainly designed to handle one or two fields. Also, you need to write custom server-side and client-side code, or maybe copy and paste code, every time you encounter validating multiple fields. To solve this, I have made this light multiple-controls validator, and got use of the new ASP.NET 2.0 features.

Background

Even with ASP.NET 2.0, a lot of valuable validation controls are missing, especially those for multiple-fields validation. Peter Blum has created a set of commercial controls called Professional Validation And More to fill this gap and he, when answering my forum post, gave me the idea of implementing my own validator.

I have also found a good article on CodeProject by Daniel Hacquebord on CustomValidator dependent on multiple controls that addresses a similar need, however, this validation control has the following advantages:

1. Doesn't require writing any client or server-side code. Just drop it on the page and assign it the controls that you want to validate.
2. HTML/XHTML compatible. It assigns additional attributes with JavaScript rather than adding them directly to the span tag. That is, it uses JavaScript document["MyMultipleFieldsValidator"].condition = "OR" rather than the HTML <span id="MyMultipleFieldsValidator" condition = "OR">.
3. Uses a .js resource file to register the client-side code rather than writing the client-side code in every page that requires this control.
4. Inherits directly from BaseValidator versus CusomValidator, thus, gaining a tiny extra performance.

There is another good article on CodeProject that gave me some inspiration, called RequiredIfValidator - Extending from the BaseValidator class about a validator that validates another field based on the selection of a drop down list.

Using the Code

BaseValidator, the base of this control, is mainly made to handle one control so I had to disable some properties that is meant to validate a single control. I had to shadow the ControlToValidate and SetFocusOnError properties and hide them from the designer and the Visual Studio editor.

[Browsable(false)]
[EditorBrowsable(EditorBrowsableState.Never)]
public new bool SetFocusOnError {
    get {
        return false;
    }
    set {
        throw new NotSupportedException("SetFocusOnError is not supported.");
    }
}

[Browsable(false)]
[EditorBrowsable(EditorBrowsableState.Never)]
public new string ControlToValidate {
    get {
        return string.Empty;
    }
    set {
        throw new NotSupportedException("ControlToValidate is not supported.");
    }
}

In the AddAttributesToRender, I am using the ASP.NET 2.0 RegisterExpandoAttribute method to add attributes, using JavaScript, to the <span> tag generated by the validator rather than adding them statically, hence, keeping it HTML/XHTML friendly.

if(this.RenderUplevel) {
    string clientID = this.ClientID;
    Page.ClientScript.RegisterExpandoAttribute(clientID, 
        "evaluationfunction", 
        "MultipleFieldsValidatorEvaluateIsValid");
    Page.ClientScript.RegisterExpandoAttribute(clientID, 
        "controlstovalidate", 
        this.GenerateClientSideControlsToValidate());
    Page.ClientScript.RegisterExpandoAttribute(clientID, 
        "condition",
        PropertyConverter.EnumToString(typeof(Conditions), Condition));
}

In the OnPreRender, I've used the new ASP.NET 2.0 method RegisterClientScriptResource to add my embedded .js file to the page. There is a good article by Gary Dryden on CodeProject called WebResource ASP.NET 2.0 explained that deals with this subject.

protected override void OnPreRender(EventArgs e) {
    base.OnPreRender(e);
    if (base.RenderUplevel) {
        this.Page.ClientScript.RegisterClientScriptResource(
            typeof(MultipleFieldsValidator),
            "AdamTibi.Web.UI.Validators.WebUIValidationExtended.js");
    }
}

Using the Validator

To use this validator from your Visual Studio IDE, you need to add the provided .dll to the toolbox. For more information on this, check the MSDN documentation.

After dropping the validator on a webform, all you need to do is to set the ControlsToValidate property, from the Properties window, to point to the controls that you want to validate. This summarizes the generated code; however, the demo attached with the article has more examples.

The Condition property, which is set to OR by default, sets the condition that you want to apply when validating multiple fields. So, OR ensures one of the fields is filled, XOR ensures one of the fields is filled but not all of them.

<%@ Page Language="C#" AutoEventWireup="true" %>
<%@ Register TagPrefix="atv" Namespace="AdamTibi.Web.UI.Validators" 
    Assembly="AdamTibi.Web.UI.Validators" %>
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN" 
"http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head id="Head1" runat="server">
    <title></title>
</head>
<body>
<form id="form1" runat="server">
<asp:TextBox ID="txtPhone" runat="server"></asp:TextBox>
<asp:TextBox ID="txtMobile" runat="server"></asp:TextBox>
<asp:TextBox ID="txtEmail" runat="server"></asp:TextBox>
<atv:MultipleFieldsValidator ID="mfv" runat="server" Condition="OR"
    ControlsToValidate="txtPhone,txtMobile,txtEmail">
    fill at least one field</atv:MultipleFieldsValidator>
</form>
</body>
</html>

Limitations

I've only tested the validator on Internet Explorer 6 and Firefox 1.5; however, I am not using any weird JavaScript so it should work on other browsers as well. Please let me know if it worked for you.

I only need the validator to check TextBox fields so I didn't check it with other types of controls; however, in theory, it should work fine. Also, let me know if you are getting any problems.

Conclusion

I hope I made someone’s day. If you like this article, then please remember to vote. If you have any suggestions, bugs, or enhancements, then hit me with it!

History

• 10^th March, 2006 - First version
• 4^th April, 2006 - Now works with Firefox