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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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