Custom Validator For ASP.NET MVC: MustBeTrue

Recently I was working on a small project to add a checkbox for users to accept Terms and Conditions during registration. In order to use the built-in validation functions by ASP.NET MVC, I wrote a small custom validator for this: MustBeTrue.

Create MustBeTrueAttribute.cs file under Attributes folder

[AttributeUsage(AttributeTargets.Property, AllowMultiple = false, Inherited = true)]
public class MustBeTrueAttribute : ValidationAttribute, IClientValidatable
{
	// for server side validation
	public override bool IsValid(object value)
	{
		return value is bool && (bool)value;
	}

	// add data- to elements for client side validation
	public IEnumerable<ModelClientValidationRule> GetClientValidationRules(ModelMetadata metadata, ControllerContext context)
	{
		var clientValidationRule = new ModelClientValidationRule()
		{
			ErrorMessage = FormatErrorMessage(metadata.GetDisplayName()),
			ValidationType = "mustbetrue"
		};
		return new[] { clientValidationRule };
	}
}

Create an adapter for Unobtrusive: jquery.validate.unobtrusive.mustbetrue.js

(function ($) {
    $.validator.addMethod("mustbetrue", function (value, element, params) {
		//check whether the element is checked
		return $(element).is(":checked");
    });
    $.validator.unobtrusive.adapters.addBool("mustbetrue");
}(jQuery));

Usage in View Model

[MustBeTrue(ErrorMessage = "Please accept the Terms & Conditions.")]
[DisplayName("I accept the Terms & Conditions.")]
public bool AcceptTerms { get; set; }

Github

https://github.com/dujushi/snippets/tree/master/MustBeTrue

Github

Reference: