c# - 这是.Net 反射中的错误吗？

Question

答案是: 不，这不是错误。区别在于 ReflectedType .

所以这里真正的问题是:有没有一种方法可以比较两个 PropertyInfo 对象，对于相同的属性，但是从不同的类型反射(reflect)出来，以便它返回 真？

原始问题

此代码通过使用两种不同的方式，为完全相同的属性 生成两个PropertyInfo 对象。结果，这些属性信息以某种方式比较不同。我花了一些时间试图弄清楚这一点。

我做错了什么？

using System;
using System.Linq;
using System.Linq.Expressions;
using System.Reflection;

namespace TestReflectionError
{
    class Program
    {
        static void Main(string[] args)
        {
            Console.BufferWidth = 200;
            Console.WindowWidth = 200;

            Expression<Func<object>> expr = () => ((ClassA)null).ValueA;
            PropertyInfo pi1 = (((expr as LambdaExpression)
                .Body as UnaryExpression)
                .Operand as MemberExpression)
                .Member as PropertyInfo;

            PropertyInfo pi2 = typeof(ClassB).GetProperties()
                .Where(x => x.Name == "ValueA").Single();

            Console.WriteLine("{0}, {1}, {2}, {3}, {4}", pi1, pi1.DeclaringType, pi1.MemberType, pi1.MetadataToken, pi1.Module);
            Console.WriteLine("{0}, {1}, {2}, {3}, {4}", pi2, pi2.DeclaringType, pi2.MemberType, pi2.MetadataToken, pi2.Module);

            // these two comparisons FAIL
            Console.WriteLine("pi1 == pi2: {0}", pi1 == pi2);
            Console.WriteLine("pi1.Equals(pi2): {0}", pi1.Equals(pi2));

            // this comparison passes
            Console.WriteLine("pi1.DeclaringType == pi2.DeclaringType: {0}", pi1.DeclaringType == pi2.DeclaringType);
            Console.ReadKey();
        }
    }

    class ClassA
    {
        public int ValueA { get; set; }
    }

    class ClassB : ClassA
    {
    }
}

这里的输出是:

Int32 ValueA, TestReflectionError.ClassA, Property, 385875969, TestReflectionError.exe
Int32 ValueA, TestReflectionError.ClassA, Property, 385875969, TestReflectionError.exe
pi1 == pi2: False
pi1.Equals(pi2): False
pi1.DeclaringType == pi2.DeclaringType: True

罪魁祸首:PropertyInfo.ReflectedType

我发现这两个对象之间存在差异......它在 ReflectedType 中。文档是这样说的:

Gets the class object that was used to obtain this member.

Answer 1

你为什么不直接比较 MetadataToken 和 Module.

根据该组合唯一标识的文档。

MemberInfo.MetadataToken
一个值，与 Module 结合使用，唯一标识元数据元素。

static void Main(string[] args)
{
    Console.BufferWidth = 200;
    Console.WindowWidth = 140;

    PropertyInfo pi1 = typeof(ClassA).GetProperties()
        .Where(x => x.Name == "ValueA").Single();
    PropertyInfo pi2 = typeof(ClassB).GetProperties()
        .Where(x => x.Name == "ValueA").Single();
    PropertyInfo pi0 = typeof(ClassA).GetProperties()
        .Where(x => x.Name == "ValueB").Single();
    PropertyInfo pi3 = typeof(ClassB).GetProperties()
        .Where(x => x.Name == "ValueB").Single();
    PropertyInfo pi4 = typeof(ClassC).GetProperties()
        .Where(x => x.Name == "ValueA").Single();
    PropertyInfo pi5 = typeof(ClassC).GetProperties()
        .Where(x => x.Name == "ValueB").Single();


    Console.WriteLine("{0}, {1}, {2}, {3}, {4}, {5}", pi1, pi1.ReflectedType, pi1.DeclaringType, pi1.MemberType, pi1.MetadataToken, pi1.Module);
    Console.WriteLine("{0}, {1}, {2}, {3}, {4}, {5}", pi2, pi2.ReflectedType, pi2.DeclaringType, pi2.MemberType, pi2.MetadataToken, pi2.Module);
    Console.WriteLine("{0}, {1}, {2}, {3}, {4}, {5}", pi0, pi0.ReflectedType, pi0.DeclaringType, pi0.MemberType, pi0.MetadataToken, pi1.Module);
    Console.WriteLine("{0}, {1}, {2}, {3}, {4}, {5}", pi3, pi3.ReflectedType, pi3.DeclaringType, pi3.MemberType, pi3.MetadataToken, pi3.Module);
    Console.WriteLine("{0}, {1}, {2}, {3}, {4}, {5}", pi4, pi4.ReflectedType, pi4.DeclaringType, pi4.MemberType, pi4.MetadataToken, pi4.Module);
    Console.WriteLine("{0}, {1}, {2}, {3}, {4}, {5}", pi5, pi5.ReflectedType, pi5.DeclaringType, pi5.MemberType, pi5.MetadataToken, pi5.Module);

    // these two comparisons FAIL
    Console.WriteLine("pi1 == pi2: {0}", pi1 == pi2);
    Console.WriteLine("pi1.Equals(pi2): {0}", pi1.Equals(pi2));

    // this comparison passes
    Console.WriteLine("pi1.DeclaringType == pi2.DeclaringType: {0}", pi1.DeclaringType == pi2.DeclaringType);


    pi1 = typeof(ClassA).GetProperties()
        .Where(x => x.Name == "ValueB").Single();

    pi2 = typeof(ClassB).GetProperties()
        .Where(x => x.Name == "ValueB").Single();

    Console.WriteLine("{0}, {1}, {2}, {3}, {4}, {5}", pi1, pi1.ReflectedType, pi1.DeclaringType, pi1.MemberType, pi1.MetadataToken, pi1.Module);
    Console.WriteLine("{0}, {1}, {2}, {3}, {4}, {5}", pi2, pi2.ReflectedType, pi2.DeclaringType, pi2.MemberType, pi2.MetadataToken, pi2.Module);

    // these two comparisons FAIL
    Console.WriteLine("pi1 == pi2: {0}", pi1 == pi2);
    Console.WriteLine("pi1.Equals(pi2): {0}", pi1.Equals(pi2));


    Console.ReadKey();
}
class ClassA
{
    public int ValueA { get; set; }
    public int ValueB { get; set; }
}
class ClassB : ClassA
{
    public new int ValueB { get; set; } 
}
class ClassC
{
    public int ValueA { get; set; }
    public int ValueB { get; set; }
}