Run time Conditional Validation (Required Field) in MVC 3.0 - asp.net-mvc

Question

I have few Address line fields in my Model class, which changes its behavior (Required / not Required) based on the selected country / language.
For example UK should have 3 address line as Required input field, where as in case of US, it should be only 2 Required fields.
I have tried to use a custom validator "RequiredIf" & turning it on or off based on another nullable Boolean property; But its not working.
Concerned property of my Model is mentioed as floows:
public bool? IsAddressLine3Mandatory { get; set; }
[RequiredIf("IsAddressline3Mandatory", true, ErrorMessage = "Address line 3 is mandatory for UK")]
public string AddressLine3 { get; set; }
I am fetching the country information from our Database & setting the IsAddressline3Mandatory field in the HTTPGet Action method for that view.
I am trying to achieve both client side & server side validation to happen.
Code for RequiredIf goes as follows:
public class RequiredIfAttribute : ValidationAttribute, IClientValidatable
{
private RequiredAttribute _innerAttribute = new RequiredAttribute();
public string DependentProperty { get; set; }
public object TargetValue { get; set; }
public RequiredIfAttribute(string dependentProperty, object targetValue)
{
this.DependentProperty = dependentProperty;
this.TargetValue = targetValue;
}
protected override ValidationResult IsValid(object value, ValidationContext validationContext)
{
// get a reference to the property this validation depends upon
var containerType = validationContext.ObjectInstance.GetType();
var field = containerType.GetProperty(this.DependentProperty);
if (field != null)
{
// get the value of the dependent property
var dependentvalue = field.GetValue(validationContext.ObjectInstance, null);
// compare the value against the target value
if ((dependentvalue == null && this.TargetValue == null) ||
(dependentvalue != null && dependentvalue.Equals(this.TargetValue)))
{
// match => means we should try validating this field
if (!_innerAttribute.IsValid(value))
// validation failed - return an error
return new ValidationResult(this.ErrorMessage, new[] { validationContext.MemberName });
}
}
return ValidationResult.Success;
}
public IEnumerable<ModelClientValidationRule> GetClientValidationRules(ModelMetadata metadata, ControllerContext context)
{
var rule = new ModelClientValidationRule()
{
ErrorMessage = FormatErrorMessage(metadata.GetDisplayName()),
ValidationType = "requiredif",
};
string depProp = BuildDependentPropertyId(metadata, context as ViewContext);
// find the value on the control we depend on;
// if it's a bool, format it javascript style
// (the default is True or False!)
string targetValue = (this.TargetValue ?? "").ToString();
if (this.TargetValue.GetType() == typeof(bool))
targetValue = targetValue.ToLower();
rule.ValidationParameters.Add("dependentproperty", depProp);
rule.ValidationParameters.Add("targetvalue", targetValue);
yield return rule;
}
private string BuildDependentPropertyId(ModelMetadata metadata, ViewContext viewContext)
{
// build the ID of the property
string depProp = viewContext.ViewData.TemplateInfo.GetFullHtmlFieldId(this.DependentProperty);
// unfortunately this will have the name of the current field appended to the beginning,
// because the TemplateInfo's context has had this fieldname appended to it. Instead, we
// want to get the context as though it was one level higher (i.e. outside the current property,
// which is the containing object (our Person), and hence the same level as the dependent property.
var thisField = metadata.PropertyName + "_";
if (depProp.StartsWith(thisField))
// strip it off again
depProp = depProp.Substring(thisField.Length);
return depProp;
}
}