使用扩展方法访问字段上的属性

Question

我想通过使用扩展方法检查我的类成员(仅限字段)上的自定义属性.

public class DatabaseIdAttribute : Attribute
{
    public int ID { get; set; }

    public DatabaseIdAttribute(int id)
    {
        this.ID = id;
    }
}

public class MyClass 
{
    [DatabaseId(1)]
    double Height {get;set;}

    [DatabaseId(2)]
    double Width {get;set;}

    double Area { get { return this.Height * this.Width; }
}

我想在扩展方法中使用LINQ表达式来访问类字段而不是传递魔术字符串.

var myClass = new MyClass();
var attribute = myClass.GetAttribute<DatabaseIdAttribute>(c => c.Height);

有可能实现吗？

[编辑]

目前,我已经在@leppie的帮助下取得了以下成绩

    public static MemberInfo GetMember<T, R>(this T instance, Expression<Func<T, R>> selector)
    {
        var member = selector.Body as MemberExpression;
        if (member != null)
        {
            return member.Member;
        }
        return null;
    }

    public static T GetAttribute<T>(this MemberInfo member) where T : Attribute
    {
        return member.GetCustomAttributes(false).OfType<T>().SingleOrDefault();
    }

这使得能够以下列方式获取属性

var c = new MyClass();
var attribute = c.GetMember(m => m.Height).GetAttribute<DatabaseIdAttribute>();

但我希望能够以下列方式访问它

var c = new MyClass();
var attribute = c.GetAttribute<DatabaseIdAttribute>(m => m.Height);

Answer 1

你快到了!这应该工作(未经测试).

public static class ObjectExtensions
{
    public static MemberInfo GetMember<T,R>(this T instance, 
         Expression<Func<T, R>> selector)
    {
        var member = selector.Body as MemberExpression;
        if (member != null)
        {
            return member.Member;
        }
        return null;
    }

    public static T GetAttribute<T>(this MemberInfo meminfo) where T : Attribute
    {
       return meminfo.GetCustomAttributes(typeof(T)).FirstOrDefault() as T;
    }
}

用法:

var attr = someobject.GetMember(x => x.Height).
              GetAttribute<DatabaseIdAttribute>();

IIRC:GetAttribute<T>(this MemberInfo meminfo)已经被定义为.NET 4中的扩展方法.