C#中使用反射以及特性简化的实例代码-木庄网络博客

本文摘自PHP中文网，作者黄舟，侵删。

假设现在有一个学生类（Student)

{  { name = 
 
Age { ;  
 
Address { ;

如果需要判断某些字段（属性）是否为空，是否大于0，便有以下代码：

public static string ValidateStudent(Student student)
        {
            StringBuilder validateMessage = new StringBuilder();            
            if (string.IsNullOrEmpty(student.Name))
            {
                validateMessage.Append("名字不能为空");
            }            if (string.IsNullOrEmpty(student.Sex))
            {
                validateMessage.Append("性别不能为空");
            }            if (student.Age <= 0)
            {
                validateMessage.Append("年龄必填大于0");
            }            
            //...... 几百行            
            // 写到这里发现不对啊，如果必填项有20多个，难道我要一直这样写吗！
            return validateMessage.ToString();
        }

这样的代码，重用性不高，而且效率低。

我们可以用特性，反射，然后遍历属性并检查特性。

首先自定义一个【必填】特性类，继承自Attribute

/// <summary>
/// 【必填】特性，继承自Attribute    /// </summary>
public sealed class RequireAttribute : Attribute
{        private bool isRequire;        public bool IsRequire
    {            get { return isRequire; }
    }        /// <summary>
    /// 构造函数        /// </summary>
    /// <param name="isRequire"></param>
    public RequireAttribute(bool isRequire)
    {            this.isRequire = isRequire;
    }
}

然后用这个自定义的特性标记学生类的成员属性：

/// <summary>
    /// 学生类    /// </summary>
    public class Student
    {   
        /// <summary>
        /// 名字        /// </summary>
        private string name;
        [Require(true)]        public string Name
        {            get { return name; }            set { name = value; }
        }        /// <summary>
        /// 年龄        /// </summary>
        [Require(true)]        public int Age { get; set; }        /// <summary>
        /// 地址        /// </summary>
        [Require(false)]        public string Address { get; set; }        /// <summary>
        /// 性别        /// </summary>
        [Require(true)] 
        public string Sex;
    }

通过特性检查类的属性：

/// <summary>
      /// 检查方法，支持泛型        /// </summary>
      /// <typeparam name="T"></typeparam>
      /// <param name="instance"></param>
      /// <returns></returns>
      public static string CheckRequire<T>(T instance)
      {            
      var validateMsg = new StringBuilder();            
      //获取T类的属性
          Type t = typeof (T);            
          var propertyInfos = t.GetProperties();            
          //遍历属性
          foreach (var propertyInfo in propertyInfos)
          {                
          //检查属性是否标记了特性
              RequireAttribute attribute = (RequireAttribute) Attribute.GetCustomAttribute(propertyInfo, typeof (RequireAttribute));                
              //没标记，直接跳过
              if (attribute == null)
              {                    
              continue;
              }                
              //获取属性的数据类型
              var type = propertyInfo.PropertyType.ToString().ToLower();                
              //获取该属性的值
              var value = propertyInfo.GetValue(instance);                
              if (type.Contains("system.string"))
              {                    
              if (string.IsNullOrEmpty((string) value) && attribute.IsRequire)
                      validateMsg.Append(propertyInfo.Name).Append("不能为空").Append(",");
              }                
              else if (type.Contains("system.int"))
              {                    
              if ((int) value == 0 && attribute.IsRequire)
                      validateMsg.Append(propertyInfo.Name).Append("必须大于0").Append(",");
              }
          }            return validateMsg.ToString();
      }

执行验证：

static void Main(string[] args)
        {            var obj = new Student()
            {
                Name = ""
            };
            Console.WriteLine(CheckRequire(obj));
            Console.Read();
        }