读取覆盖属性属性

Question

我已经覆盖类中的属性，并希望读取自定义属性值，但它不起作用。任何人都可以解释为什么它不工作，以及如何解决问题？

public class Validator 
    { 


     [Serializable] 
     public class CollectionAttribute : Attribute 
     { 
      public virtual string[] Data { get; set; } 
      public string Default; 
     } 
} 

class Helpers 
    { 

     public static MemberInfo GetMemberInfo<T, TU>(Expression<Func<T, TU>> expression) 
     { 
      var member = expression.Body as MemberExpression; 
      if (member != null) 
       return member.Member; 

      throw new ArgumentException("Expression is not a member access", "expression"); 
     } 

     public static string GetName<T, TU>(Expression<Func<T, TU>> expression) 
     { 
      return GetMemberInfo(expression).Name; 
     } 

     public static string GetCollection<T, TU>(Expression<Func<T, TU>> expression) 
     { 
      var attribute = (Validator.CollectionAttribute[])GetMemberInfo(expression).GetCustomAttributes(typeof(Validator.CollectionAttribute), true); 
      return string.Join(",", attribute[0].Data); 
     } 
    } 

不工作。

public class TestClass:TestBaseClass 
    { 
     [Validator.Collection(Data = new[] { "doc", "docx", "dot", "dotx", "wpd", "wps", "wri" })] 
     public override string InputFormat { get; set; } 
    } 

    public class TestBaseClass 
    { 
     public virtual string InputFormat { get; set; } 
    } 

Helpers.GetCollection((TestClass p) => p.InputFormat) 
//The attribute variable in GetCollection method always null. It seems code looks for atribute in Base class. 

工作正常。

public class TestClass 
    { 
     [Validator.Collection(Data = new[] { "doc", "docx", "dot", "dotx", "wpd", "wps", "wri" })] 
     public override string InputFormat { get; set; } 
    } 

Helpers.GetCollection((TestClass p) => p.InputFormat) 

Answer 1

的InputFormat声明类型是TestBaseClass不具有该属性。而PropertyInfo返回的是声明类型，而不是参数的实际类型。

您需要做的是检索表达式参数的实际类型，然后返回该类型的PropertyInfo。

public static MemberInfo GetMemberInfo<T, TU>(Expression<Func<T, TU>> expression) 
{ 
    var member = expression.Body as MemberExpression; 
    if (member != null) 
    { 
     // Getting the parameter's actual type, and retrieving the PropertyInfo for that type. 
     return expression.Parameters.First().Type.GetProperty(member.Member.Name); 
    } 

    throw new ArgumentException("Expression is not a member access", "expression"); 
}