如何在自定义验证属性中访问 viewmodel 的属性值以更改消息？

Question

viewmodel 有许多字符串属性，例如Sample，如下所示。我的要求是根据我的视图模型中的布尔标志显示不同的验证消息。该标志是IsProposer 属性，如下所述：

[SampleAttribute(true, "bla prop", "foo add driver")]       
public string Sample { get; set; }

public bool IsProposer { get; set; }

我想创建一个验证属性，这样我就可以将它放在我所有的字符串属性上（需要验证）。然后根据该布尔标志的值，我将相应地传递消息。我的自定义验证属性如下：

[AttributeUsage(AttributeTargets.Property, AllowMultiple = true, Inherited = false)]
    public class SampleAttribute : RequiredAttribute
    {
        protected string ProposerErrorMessage { get; set; }
        protected string AdditionalDriverErrorMessage { get; set; }
        protected bool IsProposer { get; set; }
        public SampleAttribute(bool isProposer, string propmsg, string adddrivermsg)
        {
            ProposerErrorMessage = propmsg;
            IsProposer = isProposer;
            AdditionalDriverErrorMessage = adddrivermsg;

        }

        protected override ValidationResult IsValid(object value, ValidationContext validationContext)
        {
            if (IsValid(value))
            {
                return ValidationResult.Success;
            }
            else
            {
                return new ValidationResult(IsProposer ? ProposerErrorMessage : AdditionalDriverErrorMessage);
            }
        }
    }

现在的问题是，如您所见，我只是将 true 作为属性的第一个参数传递。在这里，我需要从 viewmodel 实例中传递 Isproposer 属性的值，以便我可以采取相应的行动。如何访问它？

Answer 1

我通过创建这样的属性解决了我的问题：

 /// <summary>
    /// This validation attribute is an extension to RequiredAttribute that can be used to choose either of the two 
    /// validation messages depending on a property in the context of same model.
    /// </summary>
    [AttributeUsage(AttributeTargets.Property, AllowMultiple = true, Inherited = false)]
    public class RequiredExtensionAttribute : RequiredAttribute
    {
        private string _errorMessageIfTruthy;
        private string _errorMessageIfFalsy; 
        private string _dependentProperty;

        public RequiredExtensionAttribute(string dependentproperty, string errorMessageIfTruthy, string errorMessageIfFalsy)
        {
            _errorMessageIfTruthy = errorMessageIfTruthy;
            _dependentProperty = dependentproperty;
            _errorMessageIfFalsy = errorMessageIfFalsy;

        }

        protected override ValidationResult IsValid(object value, ValidationContext validationContext)
        {
            var propertyTestedInfo = validationContext.ObjectType.GetProperty(this._dependentProperty);
            if (propertyTestedInfo == null)
            {
                return new ValidationResult(string.Format("unknown property {0}", this._dependentProperty));
            }

            var propertyTestedValue = propertyTestedInfo.GetValue(validationContext.ObjectInstance, null);

            if (IsValid(value))
            {
                return ValidationResult.Success;
            }
            else
            {
                return new ValidationResult((bool)propertyTestedValue ? _errorMessageIfTruthy : _errorMessageIfFalsy);
            }
        }
    }

现在可以在以下模型中使用：

[RequiredExtensionAttribute("IsProposerViewModel", "Please select your employment status.", "Please select this driver's employment status")]       
public string EmploymentStatus { get; set; }
public bool IsProposerViewModel { get; set; }

-属性的第一个参数是IsProposerViewModel，即依赖值。