How to handle Booleans/CheckBoxes in ASP.NET MVC 2 with DataAnnotations?

Solution 1:

My Solution is as follows (it's not much different to the answers already submitted, but I believe it's named better):

/// <summary>
/// Validation attribute that demands that a boolean value must be true.
/// </summary>
[AttributeUsage(AttributeTargets.Property, AllowMultiple = false, Inherited = false)]
public class MustBeTrueAttribute : ValidationAttribute
{
    public override bool IsValid(object value)
    {
        return value != null && value is bool && (bool)value;
    }
}

Then you can use it like this in your model:

[MustBeTrue(ErrorMessage = "You must accept the terms and conditions")]
[DisplayName("Accept terms and conditions")]
public bool AcceptsTerms { get; set; }

Solution 2:

I would create a validator for both Server AND Client side. Using MVC and unobtrusive form validation, this can be achieved simply by doing the following:

Firstly, create a class in your project to perform the server side validation like so:

public class EnforceTrueAttribute : ValidationAttribute, IClientValidatable
{
    public override bool IsValid(object value)
    {
        if (value == null) return false;
        if (value.GetType() != typeof(bool)) throw new InvalidOperationException("can only be used on boolean properties.");
        return (bool)value == true;
    }

    public override string FormatErrorMessage(string name)
    {
        return "The " + name + " field must be checked in order to continue.";
    }

    public IEnumerable<ModelClientValidationRule> GetClientValidationRules(ModelMetadata metadata, ControllerContext context)
    {
        yield return new ModelClientValidationRule
        {
            ErrorMessage = String.IsNullOrEmpty(ErrorMessage) ? FormatErrorMessage(metadata.DisplayName) : ErrorMessage,
            ValidationType = "enforcetrue"
        };
    }
}

Following this, annotate the appropriate property in your model:

[EnforceTrue(ErrorMessage=@"Error Message")]
public bool ThisMustBeTrue{ get; set; }

And Finally, enable client side validation by adding the following script to your View:

<script type="text/javascript">
    jQuery.validator.addMethod("enforcetrue", function (value, element, param) {
        return element.checked;
    });
    jQuery.validator.unobtrusive.adapters.addBool("enforcetrue");
</script>

Note: We already created a method GetClientValidationRules which pushes our annotation to the view from our model.

Solution 3:

I got it by creating a custom attribute:

public class BooleanRequiredAttribute : RequiredAttribute 
{
    public override bool IsValid(object value)
    {
        return value != null && (bool) value;
    }
}

Solution 4:

This might be a "hack" but you can use the built in Range attribute:

[Display(Name = "Accepted Terms Of Service")]
[Range(typeof(bool), "true", "true")]
public bool Terms { get; set; }

The only problem is the "warning" string will say "The FIELDNAME must be between True and true".

Solution 5:

[Compare("Remember", ErrorMessage = "You must accept the terms and conditions")]
public bool Remember { get; set; }