9

我有一些将 2 个 PropertyInfos 与 Equals() 进行比较的代码。虽然这通常似乎可行,但我遇到了一种奇怪的情况,即同一基础属性的两个反射属性信息对象不相等:

PropertyInfo prop1, prop2; // both are public and not static
Console.WriteLine(prop1 == prop2); // false ???
Console.WriteLine(Equals(prop1, prop2)); // false ???
Console.WriteLine(prop1.DeclaringType == prop2.DeclaringType); // true
Console.WriteLine(prop1.ReturnType == prop2.ReturnType); // true
Console.WriteLine(prop1.Name == prop2.Name); // true
Console.WriteLine(prop1.DeclaringType.GetProperties().Contains(prop1)); // true
Console.WriteLine(prop2.DeclaringType.GetProperties().Contains(prop2)); // false ???

看起来 PropertyInfo 实际上并没有实现 Equals(),但我认为 .NET 缓存了反射成员,以便始终返回相同的实例。你肯定会一直看到 a.GetType() == b.GetType() 。这不是 PropertyInfos 的情况吗?

其他一些注意事项: - 在 .NET 4、VS2012、x86 构建目标中运行 NUnit 测试时发生了这种奇怪现象 - 我们以这种方式比较的所有属性甚至都不会发生这种情况,但它在一个属性上始终失败。

谁能解释这种行为?

编辑:如果有人感兴趣,这里是我写的比较 MemberInfos 的 EqualityComparison 函数:

public class MemberEqualityComparer : EqualityComparer<MemberInfo> {
    public override bool Equals(MemberInfo @this, MemberInfo that) {
        if (@this == that) { return true; }
        if (@this == null || that == null) { return false; }

                        // handles everything except for generics
                    if (@this.MetadataToken != that.MetadataToken
                        || !Equals(@this.Module, that.Module)
                        || this.Equals(@this.DeclaringType, that.DeclaringType))
                    {
                        return false;
                    }

                    bool areEqual;
                    switch (@this.MemberType)
                    {
                        // constructors and methods can be generic independent of their types,
                        // so they are equal if they're generic arguments are equal
                        case MemberTypes.Constructor:
                        case MemberTypes.Method:
                            var thisMethod = @this as MethodBase;
                            var thatMethod = that as MethodBase;
                                                areEqual = thisMethod.GetGenericArguments().SequenceEqual(thatMethod.GetGenericArguments(), 
this);
                            break;
                        // properties, events, and fields cannot be generic independent of their types,
                        // so if we've reached this point without bailing out we just return true.
                        case MemberTypes.Property:
                        case MemberTypes.Event:
                        case MemberTypes.Field:
                            areEqual = true;
                            break;
                        // the system guarantees reference equality for types, so if we've reached this point
                        // without returning true the two are not equal
                        case MemberTypes.TypeInfo:
                        case MemberTypes.NestedType:
                            areEqual = false;
                            break;
                        default:
                            throw new NotImplementedException(@this.MemberType.ToString());
    }

    public override int GetHashCode(MemberInfo memberInfo) {
        if (memberInfo == null) { return 0; }

    var hash = @this.MetadataToken 
        ^ @this.Module.GetHashCode() 
        ^ this.GetHashCode(@this.DeclaringType);
    return hash;
    }
}
4

2 回答 2

14

对象标识只承诺用于 Type 类,而不用于其他反射类。比较相等性的一种可能合理的方法是检查属性是否具有相同的元数据标记并且来自同一模块。所以试试这个:

bool equal = prop1.MetadataToken == prop2.MetadataToken &&
             prop1.Module.Equals(prop2.Module);

只要 ecma 335 适用,这是有道理的。由于您没有发布它,因此我无法针对您的代码进行测试。所以就试试吧。

于 2012-11-28T23:42:15.203 回答
7

我猜他们有不同的ReflectedType. 例如继承:

class A {
   public int Foo {get;set;}
}
class B : A {}

现在看看typeof(A).GetProperty("Foo")typeof(B).GetProperty("Foo")

于 2012-11-28T23:06:16.753 回答