如何在自定义验证属性中访问viewmodel的属性值来更改消息？

Question

viewmodel有许多字符串属性Sample,如下所示.我的要求是根据我的viewmodel中的bool标志显示不同的验证消息.该旗帜是 IsProposer如下所述的财产:

[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,以便我可以将它放在我的所有字符串属性上(必需的验证).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);
            }
        }
    }

现在问题是,正如您所看到的,我只是将true作为属性的第一个参数传递.在这里,我需要Isproposer从viewmodel实例传递属性的值,以便我可以相应地执行操作.我该如何访问它？

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依赖值.