C# ASP.NET MVC RequiredIf -如何将ErrorMessage设置为其他(字符串)属性的值？

using System;
using System.ComponentModel.DataAnnotations;

public class RequiredIfAttribute : ValidationAttribute
{
    private string _otherProperty;
    private string _otherPropertyValue;

    public RequiredIfAttribute(string otherProperty, string otherPropertyValue)
    {
        _otherProperty = otherProperty;
        _otherPropertyValue = otherPropertyValue;
    }

    protected override ValidationResult IsValid(object value, ValidationContext validationContext)
    {
        var otherPropertyInfo = validationContext.ObjectType.GetProperty(_otherProperty);
        var otherPropertyValue = otherPropertyInfo.GetValue(validationContext.ObjectInstance);

        if (otherPropertyValue.ToString() == _otherPropertyValue && value == null)
        {
            return new ValidationResult(ErrorMessage);
        }

        return ValidationResult.Success;
    }
}

public class YourModel
{
    [RequiredIf("OtherProperty", "OtherValue", ErrorMessage = "This field is required.")]
    public string YourProperty { get; set; }

    public string OtherProperty { get; set; }
    public string OtherValue { get; set; }
}

@model YourModel

@using (Html.BeginForm())
{
    @Html.LabelFor(m => m.YourProperty)
    @Html.TextBoxFor(m => m.YourProperty)
    @Html.ValidationMessageFor(m => m.YourProperty)

    <input type="submit" value="Submit" />
}