C#自定義Attribute值的獲取與優化

　　C#自定義Attribute值的獲取是開發中會經常用到的，一般我們的做法也就是用反射進行獲取的，代碼也不是很復雜。

      1、首先有如下自定義的Attribute

    [AttributeUsage(AttributeTargets.All)]
    public sealed class NameAttribute : Attribute
    {
        private readonly string _name;

        public string Name
        {
            get { return _name; }
        }

        public NameAttribute(string name)
        {
            _name = name;
        }
    }

　　2、定義一個使用NameAttribute的類

[Description("Customer Information")]
[Name("customer_info")]
public class CustomerInfo
{
    [Name("name")]
    public string Name { get; set; }

    [Name("address")]
    public string Address;
}

　

　　3、獲取CustomAttributes類上的"dept"也就很簡單了

        private static string GetName()
        {
            var type = typeof(CustomAttributes);

            var attribute = type.GetCustomAttributes(typeof(NameAttribute), false).FirstOrDefault();

            if (attribute == null)
            {
                return null;
            }

            return ((NameAttribute)attribute).Name;
        }

　　以上代碼就可以簡單的獲取，類上的Attribute的值了，但是需求往往不是這么簡單的，不僅要獲取類頭部Attribute上的值，還要獲取字段Address頭部Attribute上的值。有的同學可能就覺得這還不簡單呀，直接上代碼

        private static string GetAddress()
        {
            var type = typeof (CustomAttributes);

            var fieldInfo = type.GetField("Address");
            if (fieldInfo == null)
            {
                return null;
            }

            var attribute = fieldInfo.GetCustomAttributes(typeof(NameAttribute), false).FirstOrDefault();

            if (attribute == null)
            {
                return null;
            }

            return ((NameAttribute) attribute).Name;
        }

　　上面代碼就是獲取Address字段頭部上的Attribute值了。雖然我們是獲取到了我們想要的，但是我們發現這樣做是不是太累了，如果又擴展一個自定義的Attribute，或者又在一個新的屬性或字段上標上Attribute時，我們又要寫一段代碼來實現我想要的，這些嚴重代碼違反了DRY的設計原則。我們知道獲取Attribute是通過反射來取的，Attribute那個值又是不變的，這樣就沒必要每次都要進行反射來獲取了。基於以上兩點代碼進行了如下的優化，優化后的代碼如下：

 

using System;
using System.Collections.Concurrent;
using System.Reflection;

public static class CustomAttributeExtensions
{
    /// <summary>
    /// Cache Data
    /// </summary>
    private static readonly ConcurrentDictionary<string, object> Cache = new ConcurrentDictionary<string, object>();

    /// <summary>
    /// 獲取CustomAttribute Value
    /// </summary>
    /// <typeparam name="TAttribute">Attribute的子類型</typeparam>
    /// <typeparam name="TReturn">TReturn的子類型</typeparam>
    /// <param name="sourceType">頭部標有CustomAttribute類的類型</param>
    /// <param name="attributeValueAction">取Attribute具體哪個屬性值的匿名函數</param>
    /// <returns>返回Attribute的值，沒有則返回null</returns>
    public static TReturn GetCustomAttributeValue<TAttribute, TReturn>(this Type sourceType, Func<TAttribute, TReturn> attributeValueAction)
        where TAttribute : Attribute
    {
        return _getAttributeValue(sourceType, attributeValueAction, null);
    }

    /// <summary>
    /// 獲取CustomAttribute Value
    /// </summary>
    /// <typeparam name="TAttribute">Attribute的子類型</typeparam>
    /// <typeparam name="TReturn">TReturn的子類型</typeparam>
    /// <param name="sourceType">頭部標有CustomAttribute類的類型</param>
    /// <param name="attributeValueAction">取Attribute具體哪個屬性值的匿名函數</param>
    /// <param name="propertyName">field name或property name</param>
    /// <returns>返回Attribute的值，沒有則返回null</returns>
    public static TReturn GetCustomAttributeValue<TAttribute, TReturn>(this Type sourceType, Func<TAttribute, TReturn> attributeValueAction, string propertyName)
        where TAttribute : Attribute
    {
        return _getAttributeValue(sourceType, attributeValueAction, propertyName);
    }

    #region private methods

    private static TReturn _getAttributeValue<TAttribute, TReturn>(Type sourceType, Func<TAttribute, TReturn> attributeFunc, string propertyName)
        where TAttribute : Attribute
    {
        var cacheKey = BuildKey<TAttribute>(sourceType, propertyName);
        var value = Cache.GetOrAdd(cacheKey, k => GetValue(sourceType, attributeFunc, propertyName));
        if (value is TReturn) return (TReturn)Cache[cacheKey];
        return default(TReturn);
    }

    private static string BuildKey<TAttribute>(Type type, string propertyName) where TAttribute : Attribute
    {
        var attributeName = typeof(TAttribute).FullName;
        if (string.IsNullOrEmpty(propertyName))
        {
            return type.FullName + "." + attributeName;
        }

        return type.FullName + "." + propertyName + "." + attributeName;
    }

    private static TReturn GetValue<TAttribute, TReturn>(this Type type, Func<TAttribute, TReturn> attributeValueAction, string name)
        where TAttribute : Attribute
    {
        TAttribute attribute = default(TAttribute);
        if (string.IsNullOrEmpty(name))
        {
            attribute = type.GetCustomAttribute<TAttribute>(false);
        }
        else
        {
            var propertyInfo = type.GetProperty(name);
            if (propertyInfo != null)
            {
                attribute = propertyInfo.GetCustomAttribute<TAttribute>(false);
            }
            else
            {
                var fieldInfo = type.GetField(name);
                if (fieldInfo != null)
                {
                    attribute = fieldInfo.GetCustomAttribute<TAttribute>(false);
                }
            }
        }

        return attribute == null ? default(TReturn) : attributeValueAction(attribute);
    }

    #endregion
}

　　優化后的代碼：

　　把不同的代碼用泛型T,Fun<TAttribute,TReturn>來處理來減少重復的代碼；
　　把取過的Attribute值存到一個ConcurrentDictionary中，下次再來取時，如果有則直接取ConcurrentDictionary中的值，如果沒有才通過反射來取相應的Attribute值，這樣大大的提高效率；

　　調用方法也更加的簡單了，代碼如下：

            var customerInfoName = typeof(CustomerInfo).GetCustomAttributeValue<NameAttribute, string>(x => x.Name);
            var customerAddressName = typeof(CustomerInfo).GetCustomAttributeValue<NameAttribute, string>(x => x.Name, "Address");
            var customerInfoDesc = typeof(CustomerInfo).GetCustomAttributeValue<DescriptionAttribute, string>(x => x.Description);

            Console.WriteLine("CustomerInfo Name:" + customerInfoName);
            Console.WriteLine("customerInfo >Address Name:" + customerAddressName);
            Console.WriteLine("customerInfo Desc:" + customerInfoDesc);

　　運行結果：

     

　　如果你有什么好的或不好的意見歡迎拍磚!

　　謝謝大家的建議，己經更新（2019/11/21）

　　Code：Download