使用attribute + 扩展方法完成 enum中field的信息映射

attribute可用来做信息映射，比起Dictionary或者Tuple，attribute显得更灵活，解耦，并可对应多种类型

以下是一个enum中的field的信息映射

1. 创建field attribute

 [AttributeUsage(AttributeTargets.Field)]
    public class JobActionMetadatAttribute : Attribute
    {
        public JobActionUIType UIType { get; private set; }
        public string Label { get; private set; }

        public JobActionMetadatAttribute(JobActionUIType uiType, string label)
        {
            UIType = uiType;
            Label = label;
        }
    }

2.准备一个extension 方法

  public static class JobActionExtenssion
    {
        public static JobActionMetadata GetMetaData(this JobAction jobAction)
        {
            var attr = Attribute.GetCustomAttribute(jobAction.GetType().GetMember(jobAction.ToString())[0],
                typeof(JobActionMetadatAttribute));

            if (attr != null)
            {
                var props = attr.GetType().GetProperties();
                JobActionUIType uiType;
                var uiTypeObj = props.FirstOrDefault(p => p.PropertyType == typeof(JobActionUIType));

                if (uiTypeObj == null)
                {
                    throw new InvalidDataException(string.Format("Failed to find JobActionUIType Property in JobActionMetadataAttribute"));
                }

                var uiTypeStr = uiTypeObj.GetValue(attr, null).ToString();

                if (!Enum.TryParse(uiTypeStr, true, out uiType))
                {
                    throw new InvalidEnumArgumentException(string.Format("Enum Parsing failed. string : {0}", uiTypeStr));
                }

                var label = props.First(p => p.Name == "Label").GetValue(attr, null).ToString();

                return new JobActionMetadata(jobAction, uiType, label, "");
            }
            throw new InvalidDataException(string.Format("Failed to find JobActionMetadatAttribute for Action : {0}", jobAction));
        }

    }

3. 在enum的field上应用特性

 public enum JobAction
    {
        [JobActionMetadatAttribute(JobActionUIType.Success, "Paypal Payment")]
        MakePayPalSimplePayment = 0,

        [JobActionMetadatAttribute(JobActionUIType.Success, "Pay by Free Pass")]
        MakeFreePassPayment = 1,

        [JobActionMetadatAttribute(JobActionUIType.Success, "Pay by Company Credit")]
        MakeCompanyCreditPayment = 2,
    }

4. 使用

job.JobAction.GetMetaData();