c# - 将值传递给自定义属性

Question

我想自定义一个属性。说

public class IdExistAttribute : ValidationAttribute
{

    protected override ValidationResult IsValid(object value,
                                                  ValidationContext validationContext)
    {
        string id= value.ToString();
        if(ListOfId.Contains(id))
        {
           return new ValidationResult("Id is already existing");
        }

        return ValidationResult.Success;
     }
 }

问题是 ListOfId 是来自服务的，我不能在属性里面消费服务。那么如何从外部传递呢？

我想将属性用作

private string _id;
[IdExist]
public string Id
{
  get{return _id;}
  set{_id=value;}
}

Answer 1

ValidationContext通过 GetService 提供对已注册依赖项注入(inject)容器的访问。

引用 Andrew Lock :

As you can see, you are provided a ValidationContext as part of the method call. The context object contains a number of properties related to the object currently being validated, and also this handy number:

public object GetService(Type serviceType);

所以你可以像这样使用ValidationContext:

protected override ValidationResult IsValid(object value, ValidationContext validationContext)
{
    var service = (IExternalService) validationContext
                         .GetService(typeof(IExternalService));
    // use service
}