如何在自定义验证属性中访问viewmodel的属性值以更改消息? [英] How to access viewmodel's property value in custom validation attribute to alter messages?

问题描述

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

The viewmodel has many string properties like Sample as below. My requirement is to show different validation messages depending on a bool flag in my viewmodel. That flag is IsProposer property as mentioned below:

[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，以便可以将其放在我的所有字符串属性(必需的验证)上.然后根据该布尔标志的值，我将相应地传递味精.我的自定义验证属性如下:

I thought to create a validation attribute so that I can just place it on all my string properties (required validation). And then depending on the value of that boolean flag, I will pass the msg accordingly. My custom validation attribute is as follows:

[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，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，我需要从viewmodel实例传递Isproposer属性的值，以便随后可以采取相应的措施.我该如何访问?

Now the issue is, as you can see I am just passing true as first parameter for the attribute. Here, I need to pass the Isproposer property's value from the viewmodel instance so that I can then act accordingly. How can I access it?

推荐答案

我通过创建这样的属性解决了我的问题:

I solved my problem by creating a attribute like this:

 /// <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:

This can now be used in models like:

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

-其中属性的第一个参数是相关值IsProposerViewModel.

-where the first parameter for attribute is the IsProposerViewModel, the dependent value.

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