C# 特性的创建与使用

1、先创建一些特性以及一个示例类

//应用的目标类型：类，属性，或者其他，是否对同一个目标进行多次应用
    [AttributeUsage(AttributeTargets.Class | AttributeTargets.Method, AllowMultiple = false)]
    class DoseInterstingThingAttribute : Attribute
    {
        public int HowManyTimes { get; private set; }
        public string WhatDoseItDo { get; set; }

        public DoseInterstingThingAttribute(int howManyTimes)
        {
            HowManyTimes = howManyTimes;
        }
    }

    [AttributeUsage(AttributeTargets.Class | AttributeTargets.Method, AllowMultiple = false)]
    class DataBaseTypeAttribute : Attribute
    {
        public string DataTypeName { get; set; }

        public int MaxConnectiCount { get; set; }

        public DataBaseTypeAttribute(string dataTypeName)
        {
            DataTypeName = dataTypeName;
        }
    }

    [AttributeUsage(AttributeTargets.Property,AllowMultiple =false)]
    class DataAttribute : Attribute
    {
        public bool IsPrimaryKey { get; set; }
    }

    [DataBaseType("Mysql", MaxConnectiCount = 1000)]
    [DoseInterstingThing(1000)]
    public class DecoratedClass
    {
        [Data(IsPrimaryKey =false)]
        public int Code { get; set; }

        public string Name { get; set; }
    }

2、Main方法中输出

 static void Main(string[] args)
        {
            #region 特性使用
            Type classType = typeof(DecoratedClass);
            object[] customAttributes = classType.GetCustomAttributes(true);
            foreach (var customAttribute in customAttributes)
            {
                Console.WriteLine($"Attribute of type {customAttribute} found.");
                DoseInterstingThingAttribute interstingThingAttribute = customAttribute as DoseInterstingThingAttribute;
                if (interstingThingAttribute != null)
                {
                    Console.WriteLine($"This class does {interstingThingAttribute.WhatDoseItDo} x{interstingThingAttribute.HowManyTimes}");
                }
                DataBaseTypeAttribute dataBaseTypeAttribute = customAttribute as DataBaseTypeAttribute;
                if (dataBaseTypeAttribute != null)
                {
                    Console.WriteLine($"This class does {dataBaseTypeAttribute.DataTypeName}");
                }
            }

            PropertyInfo[] propertyInfo = classType.GetProperties();
            foreach (var property in propertyInfo)
            {
                object[] customAttributes_Propertys = classType.GetProperty(property.Name).GetCustomAttributes(true);
                foreach (var customAttributes_Property in customAttributes_Propertys)
                {
                    Console.WriteLine((DataAttribute)customAttributes_Property==null? $"{property.Name}不存在Data特性": ((DataAttribute)customAttributes_Property).IsPrimaryKey.ToString());
                }
            }
            #endregion
        }