How to add custom validate method for viewmodel

I tried to add custom validator for ViewModel class:

[Serializable]
public class UserViewModel : IValidatableObject 
{
    public IEnumerable<ValidationResult> Validate(ValidationContext context)
    {
        yield return new ValidationResult("Fail this validation");
    }
}

Unfortunately this is not triggered when Action 开发者_如何学JAVAmethod gets called, e.g.

    [HttpPost]
    public ActionResult Edit(UserViewModel user)

How can I add custom validation logic? ValidationAttribute does not provide easy enough solution. I am unable to find clear information on MVC2 validation mechanisms.

IValidatableObject is not supported in ASP.NET 2.0. Support for this interface was added in ASP.NET MVC 3. You could define a custom attribute:

[AttributeUsage(AttributeTargets.Class)]
public class ValidateUserAttribute : ValidationAttribute
{
    public override bool IsValid(object value)
    {
        UserViewModel user = value as UserViewModel;
        // TODO: do some validation

        ErrorMessage = "Fail this validation";
        return false;
    }
}

and then decorate your view model with this attribute:

[Serializable]
[ValidateUser]
public class UserViewModel
{

}

Your syntax looks right. The validation isn't "triggered" until you try to validate your model. Your controller code should look like this

[HttpPost]
public ActionResult Edit(UserViewModel user)
{
    if(ModelState.IsValid)
    {
        // at this point, `user` is valid
    }

    // since you always yield a new ValidationResult, your model shouldn't be valid
    return View(vm);
}