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How to require that a checkbox is selected when submitting a form in ASP.NET MVC

Learn how to correctly validate whether or not a checkbox has been selected when submitting a form in ASP.NET MVC

Posted on Wednesday, October 19, 2016 at 4:28 PM into code c# by Steve Woods

Sometimes you really need a user to put a tick in a checkbox, for instance when submitting a registration form where acceptance of terms and conditions is required.

Here's how you do it in ASP.NET MVC, via a custom ValidationAttribute that decorates a property of your ViewModel:

The Custom ValidationAttribute

public class MustBeTrueAttribute : ValidationAttribute
{
    public override bool IsValid(object value)
    {
        return value is bool && (bool)value;
    }
}

Decorating your ViewModel property

[MustBeTrue(ErrorMessage = "Please check the box before continuing!")]
public bool TandCs { get; set; }

Job done :)

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