反射 - 获取属性的属性名称和值

Question

我有一个类,让我们用名为Name的属性调用它.使用该属性,我有一个与之关联的属性.

public class Book
{
    [Author("AuthorName")]
    public string Name
    {
        get; private set; 
    }
}

在我的main方法中,我正在使用反射并希望为每个属性获取每个属性的键值对.所以在这个例子中,我希望看到属性名称为"Author",属性值为"AuthorName".

问题:如何使用Reflection获取属性的属性名称和值？

Answer 1

使用typeof(Book).GetProperties()获得的阵列PropertyInfo实例.然后GetCustomAttributes()在每个PropertyInfo上使用以查看它们中是否有任何Author属性类型.如果是,您可以从属性信息中获取属性的名称,并从属性中获取属性值.

沿着这些行扫描类型以获取具有特定属性类型的属性并返回字典中的数据(请注意,通过将类型传递到例程中可以使其更加动态化):

public static Dictionary<string, string> GetAuthors()
{
    Dictionary<string, string> _dict = new Dictionary<string, string>();

    PropertyInfo[] props = typeof(Book).GetProperties();
    foreach (PropertyInfo prop in props)
    {
        object[] attrs = prop.GetCustomAttributes(true);
        foreach (object attr in attrs)
        {
            AuthorAttribute authAttr = attr as AuthorAttribute;
            if (authAttr != null)
            {
                string propName = prop.Name;
                string auth = authAttr.Name;

                _dict.Add(propName, auth);
            }
        }
    }

    return _dict;
}

Answer 2

要获取字典中属性的所有属性,请使用以下命令:

typeof(Book)
  .GetProperty("Name")
  .GetCustomAttributes(false) 
  .ToDictionary(a => a.GetType().Name, a => a);

如果要包含继承属性,请记住将false更改为true.

Answer 3

如果您只想要一个特定的属性值对于实例显示属性,您可以使用以下代码:

var pInfo = typeof(Book).GetProperty("Name")
                             .GetCustomAttribute<DisplayAttribute>();
var name = pInfo.Name;

Answer 4

我通过编写通用扩展属性属性助手解决了类似的问题:

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

public static class AttributeHelper
{
    public static TValue GetPropertyAttributeValue<T, TOut, TAttribute, TValue>(
        Expression<Func<T, TOut>> propertyExpression, 
        Func<TAttribute, TValue> valueSelector) 
        where TAttribute : Attribute
    {
        var expression = (MemberExpression) propertyExpression.Body;
        var propertyInfo = (PropertyInfo) expression.Member;
        var attr = propertyInfo.GetCustomAttributes(typeof(TAttribute), true).FirstOrDefault() as TAttribute;
        return attr != null ? valueSelector(attr) : default(TValue);
    }
}

用法:

var author = AttributeHelper.GetPropertyAttributeValue<Book, string, AuthorAttribute, string>(prop => prop.Name, attr => attr.Author);
// author = "AuthorName"

Answer 5

你可以使用GetCustomAttributesData()和GetCustomAttributes():

var attributeData = typeof(Book).GetProperty("Name").GetCustomAttributesData();
var attributes = typeof(Book).GetProperty("Name").GetCustomAttributes(false);

Answer 6

如果您的意思是"对于带有一个参数的属性,列出属性名称和参数值",那么在.NET 4.5中通过CustomAttributeDataAPI 更容易:

using System.Collections.Generic;
using System.ComponentModel;
using System.Reflection;

public static class Program
{
    static void Main()
    {
        PropertyInfo prop = typeof(Foo).GetProperty("Bar");
        var vals = GetPropertyAttributes(prop);
        // has: DisplayName = "abc", Browsable = false
    }
    public static Dictionary<string, object> GetPropertyAttributes(PropertyInfo property)
    {
        Dictionary<string, object> attribs = new Dictionary<string, object>();
        // look for attributes that takes one constructor argument
        foreach (CustomAttributeData attribData in property.GetCustomAttributesData()) 
        {

            if(attribData.ConstructorArguments.Count == 1)
            {
                string typeName = attribData.Constructor.DeclaringType.Name;
                if (typeName.EndsWith("Attribute")) typeName = typeName.Substring(0, typeName.Length - 9);
                attribs[typeName] = attribData.ConstructorArguments[0].Value;
            }

        }
        return attribs;
    }
}

class Foo
{
    [DisplayName("abc")]
    [Browsable(false)]
    public string Bar { get; set; }
}

Answer 7

private static Dictionary<string, string> GetAuthors()
{
    return typeof(Book).GetProperties()
        .SelectMany(prop => prop.GetCustomAttributes())
        .OfType<AuthorAttribute>()
        .ToDictionary(a => a.GetType().Name.Replace("Attribute", ""), a => a.Name);
}

使用泛型的示例（目标框架 4.5）

using System;
using System.Collections.Generic;
using System.Linq;
using System.Reflection;

private static Dictionary<string, string> GetAttribute<TAttribute, TType>(
    Func<TAttribute, string> valueFunc)
    where TAttribute : Attribute
{
    return typeof(TType).GetProperties()
        .SelectMany(p => p.GetCustomAttributes())
        .OfType<TAttribute>()
        .ToDictionary(a => a.GetType().Name.Replace("Attribute", ""), valueFunc);
}

用法

var dictionary = GetAttribute<AuthorAttribute, Book>(a => a.Name);