C# 使用表达式树获取特性的值

一、定义特性

        /// <summary>
        /// 定义特性
        /// </summary>
        [AttributeUsage(AttributeTargets.Field | AttributeTargets.Class | AttributeTargets.Property, AllowMultiple = false)]
        public class DataMember : Attribute
        {
            public string Name { get; set; }

            public string Type { get; set; }
        }

二、创建工具类

利用泛型类得知要获取那个类上成员特性的类型，这样就能用Lambda表达式了。Expression.Body读取时是 System.Linq.Expressions.PropertyExpression 类型，找不到断点中Member属性。所以需要转换成 System.Linq.Expressions.MemberExpression 类型

        /// <summary>
        /// 获取特性工具类
        /// </summary>
        /// <typeparam name="T"></typeparam>
        public static class AttrTool<T>
        {
            /// <summary>
            /// 获取特性Name属性
            /// </summary>
            /// <typeparam name="Result"></typeparam>
            /// <param name="expression"></param>
            /// <returns></returns>
            public static string DataMemberName<Result>(Expression<Func<T, Result>> expression)
            {
                var body = expression.Body as MemberExpression;
                var attr = body.Member.CustomAttributes.FirstOrDefault(t => t.AttributeType == typeof(DataMember));
                var property = attr.NamedArguments.FirstOrDefault(t => t.MemberName == "Name");
                return property.TypedValue.Value.ToString();
            }
            /// <summary>
            /// 获取特性Type属性
            /// </summary>
            /// <typeparam name="Result"></typeparam>
            /// <param name="expression"></param>
            /// <returns></returns>
            public static string DataMemberType<Result>(Expression<Func<T, Result>> expression)
            {
                var body = expression.Body as MemberExpression;
                var attr = body.Member.CustomAttributes.FirstOrDefault(t => t.AttributeType == typeof(DataMember));
                var property = attr.NamedArguments.FirstOrDefault(t => t.MemberName == "Type");
                return property.TypedValue.Value.ToString();
            }

        }

三、定义测试模型及调用

        /// <summary>
        /// 测试模型
        /// </summary>
        public class AttrModel
        {
            [DataMember(Name = "this is Test", Type = "string")]
            public string Name { get; set; }
        }

        static void Main(string[] args)
        {
            var res1 = AttrTool<AttrModel>.DataMemberName(t => t.Name);
            var res2 = AttrTool<AttrModel>.DataMemberType(t => t.Name);
            Console.WriteLine(res1);
            Console.WriteLine(res2);
            Console.ReadLine();
        }

结果：

标签：FirstOrDefault,string,C#,获取,static,var,public,表达式,Name
来源： https://blog.csdn.net/qq395537505/article/details/113641611