Simplified example code using reflection and features in C#

Suppose there is a student class (Student)

    
 
     
      
         
           {  { name = 
         
          Age { ;  
         
          Address { ;

If you need to determine whether some fields (attributes) are empty, Whether it is greater than 0, there will be the following code:

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();
        }

Such code has low reusability and low efficiency.

We can use attributes, reflection, and then iterate over the properties and check the attributes.

First customize a [required] attribute class, inherited from 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;
        }
    }

Then use this customized attribute to mark the member attributes of the student class:

/// <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;
    }

Check the properties of the class by attributes:

  /// <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();
        }

Perform validation:

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

Result output:

#Some people will find that Sex is also marked [Require(true)], why there is no verification information, this is because, Sex does not implement the properties {get; set; }, and GetProperties cannot be obtained

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