Surely Required Field Validator is not going to work in this case.So we will be using Custom Validator for validation.Then, to show your error message on your client HTML you would need to set since the target of your attribute is the instance itself.I'll review your current code too, because there is three points that I see could be "better" :) By convention, attributes should end with the suffix when you use it (as shown in my example, which compiles! Also, your brackets are following the Java standard, not the C# one. NET 4.0 and C#", please follow the link below: ASP. NET Validate a Check Box with a Custom Validator in ASP.
You would loose consistency in displaying validation errors.
The value we provide as the validation type will be rendered as the name of the rule in the HTML element, and will be used further down to tell j Query how to validate this property.
After creating the new validation attribute, we need to apply it to a boolean property on out model; This just registers a new validation adapter for the boolean required attribute, where the first parameter is the adapter name and the second parameter is the name of j Query validate rule.
The adapter name should match the value we specified earlier as the validation type, and the j Query validation -rule will require the user to check the checkbox. This will make sure that the checkbox is checked by the user client-side (using j Query unobtrusive validation*) and that the boolean property is set to true server-side when the form is submitted to the server.
To view the tutorial, "Validate a Check Box with a Custom Validator in ASP.