ASP.NET Validation: Selective Validation

Teemu Keiski

When developing applications and specifying controls that provide user input, one might indeed face very customized needs to do the validation. Occasionally validation should be selective and occasionally very restricted. In this article I demonstrate how to develop custom validator control that will help to achieve selective validation utilizing also client-side techniques so that certain specified validator is enabled/disabled based on input in other control.

Overview of things developer needs to do to realize this validator:

1.      Derive the validator from BaseValidator

2.      Create “ValidatorToBeDisabled” property to specify ID of validator control, target validator, that will be enabled/disabled based on selection

3.      Create “DisableValue” property to specify the value when target validation control is disabled

4.      Create property to specify initial value that tells whether control to be validated is considered to be “empty” ie. this custom validation control will fail/pass validation

5.      Override EvaluateIsValid method to specify server-side validation logic.

6.      Override ControlPropertiesValid method to specify whether provided control ID is OK.

7.      Override OnPreRender and AddAttributesToRender methods to specify client-side validation logic when client browser is uplevel browser.

Validation logic

When the value of control to be validated equals “DisableValue”, the validator specified in “ValidatorToBeDisabled” property is disabled and Boolean value True is returned from custom validator. If the value of control to be validated does not equal “DisableValue”, it is compared to “InitialValue” to see if mandatory selections/input has been specified for control to be validated.

If not, in other words control value equals “InitialValue”, target validator is disabled and Boolean value False returned from our custom validator. Otherwise target validator is enabled, validation done and Boolean value True returned from our custom validator.

[Download code]

Usage example

<!--

Beginning of the page

//-->

<form id=WebForm6 method=post runat="server"><asp:RadioButtonList id=RadioButtonList1 runat="server">

<asp:ListItem>Work phone</asp:ListItem>

<asp:ListItem>Home phone</asp:ListItem>

<asp:ListItem Value="No phone">No phone</asp:ListItem>

</asp:RadioButtonList>

<br>
<asp:Label id=Label1 runat="server">Specify phone if you have such</asp:Label>
<asp:TextBox id=TextBox1 runat="server"></asp:TextBox>
<asp:Button id=Button1 runat="server" Text="Button"></asp:Button>
<br>

<cc2:SelectiveValidator id=SelectiveValidator1 runat="server" ControlToValidate="RadioButtonList1" DisableValue="No phone" ValidatorToBeDisabled="RequiredFieldValidator1" Display="Dynamic" ErrorMessage="Select the phone type"></cc2:SelectiveValidator>

<asp:RequiredFieldValidator id=RequiredFieldValidator1 runat="server" ErrorMessage="You must specify the phone number" ControlToValidate="TextBox1"></asp:RequiredFieldValidator>

</form>

<!--

End of the page

 //-->    

Demo

Work phone

Home phone

No phone

Specify phone if you have such