ASP.NET MVC: Adding custom ErrorMessage that incorporates DisplayName to custom ValidationAttribute

asp.net-mvc, data-annotations

Solution

slightly modified StringLengthAttribute:

public class StringRangeAttribute : ValidationAttribute
{
    // Methods
    public StringRangeAttribute(int minimumLength, int maximumLength)
        : base(() => "The {0} must be between {1} and {2} chars long.")
    {
        MaximumLength = maximumLength;
        MinimumLength = minimumLength;
    }

    public override string FormatErrorMessage(string name)
    {
        return string.Format(CultureInfo.CurrentCulture, ErrorMessageString, new object[] { name, MinimumLength ,MaximumLength });
    }

    public override bool IsValid(object value)
    {
        if (value != null)
        {
            return (((string)value).Length <= MaximumLength) && (((string)value).Length >= MinimumLength);
        }
        return true;
    }

    public int MaximumLength { get; set; }
    public int MinimumLength { get; set; }
}

Problem

I am using ASP.NET MVC with DataAnnotations. I have created the following custom ValidationAttribute which works fine. ``` public class StringRangeAttribute : ValidationAttribute { public int MinLength { get; set; } public int MaxLength { get; set; } public StringRangeAttribute(int minLength, int maxLength) { this.MinLength = (minLength < 0) ? 0 : minLength; this.MaxLength = (maxLength < 0) ? 0 : maxLength; } public override bool IsValid(object value) { //null or empty is <em>not</em> invalid string str = (string)value; if (string.IsNullOrEmpty(str)) return true; return (str.Length >= this.MinLength && str.Length <= this.MaxLength); } } ``` However, the error message that appears is the standard "The field * is invalid". I would like to change this to be: "The [DisplayName] must be between [minlength] and [maxlength]", however I cannot figure out how to get the DisplayName or even the name of the field from inside this class. Anyone know?

Original source