我可以使用自定义验证属性手动验证属性吗？

Question

我有一个自定义的ValidationAttribute ，但是我只想在选中CheckBox的情况下验证此属性。

我已经使类继承自IValidationObject并且正在使用Validate方法执行任何自定义验证，但是我可以在此处使用自定义ValidationAttribute而不是复制代码吗？ 如果是这样，怎么办？

public class MyClass : IValidatableObject
{
    public bool IsReminderChecked { get; set; }
    public bool EmailAddress { get; set; }

    public IEnumerable<ValidationResult> Validate(ValidationContext validationContext)
    {
        if (IsReminderChecked)
        {
            // How can I validate the EmailAddress field using
            // the Custom Validation Attribute found below?
        }
    }
}


// Custom Validation Attribute - used in more than one place
public class EmailValidationAttribute : ValidationAttribute
{
    public override bool IsValid(object value)
    {
        var email = value as string;

        if (string.IsNullOrEmpty(email))
            return false;

        try
        {
            var testEmail = new MailAddress(email).Address;
        }
        catch (FormatException)
        {
            return false;
        }

        return true;
    }
}

Answer 1

可以根据另一个属性的值来验证一个属性，但是要确保验证引擎按照您期望的方式工作，需要克服一些困难。 Simon Ince的RequiredIfAttribute方法很好，只需将电子邮件验证逻辑添加到IsValid方法中，就很容易将其修改为ValidateEmailIfAttribute 。

例如，您可以像现在一样拥有基本验证属性：

public class ValidateEmailAttribute : ValidationAttribute
{
  ...
}

然后使用Ince的方法定义条件版本：

public class ValidateEmailIfAttribute : ValidationAttribute, IClientValidatable
{
  private ValidateEmailAttribute _innerAttribute = new ValidateEmailAttribute();

  public string DependentProperty { get; set; }
  public object TargetValue { get; set; }

  public ValidateEmailIfAttribute(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;
  }

  // Client-side validation code omitted for brevity
}

然后，您可能会得到类似：

[ValidateEmailIf("IsReminderChecked", true)]
public bool EmailAddress { get; set; }