C#使用反射获取对象变化的情况
记录日志时, 经常需要描述对象的状态发生了怎样的变化, 以前处理的非常简单粗暴:
a. 重写class的ToString()方法, 将重要的属性都输出来
b. 记录日志时: 谁谁谁 由 变更前实例.ToString() 变成 变更后实例.ToString()
但输出的日志总是太长了, 翻看日志时想找到差异也非常麻烦, 所以想输出为: 谁谁谁的哪个属性由 aaa 变成了 bbb
手写代码一个一个的比较字段然后输出这样的日志信息, 是不敢想象的事情. 本来想参考Dapper使用 System.Reflection.Emit 发射 来提高运行效率, 但实在没有功夫研究.Net Framework的中间语言, 所以准备用 Attribute特性 和 反射 来实现
![](https://images.cnblogs.com/OutliningIndicators/ExpandedBlockStart.gif)
/// <summary> /// 要比较的字段或属性, 目前只支持C#基本类型, 比如 int, bool, string等, 你自己写的class或者struct 需要重写 ToString()、Equals(), 按理说如果重写了Equals(), 那也需要重写GetHashCode(), 但确实没有用到GetHashCode(), 所以可以忽略Warning不重写GetHashCode(); /// </summary> [AttributeUsage(AttributeTargets.Property | AttributeTargets.Field, AllowMultiple = false, Inherited = false)] public class ComparePropertyFieldAttribute : Attribute { /// <summary> /// 属性或字段的别名 /// </summary> public string PropertyName { get; private set; } /// <summary> /// 要比较的字段或属性 /// </summary> public ComparePropertyFieldAttribute() { } /// <summary> /// 要比较的字段或属性 /// </summary> /// <param name="propertyName">属性或字段的别名</param> public ComparePropertyFieldAttribute(string propertyName) { PropertyName = propertyName; } // 缓存反射的结果, Tuple<object, ComparePropertyAttribute> 中第一个参数之所以用object 是因为要保存 PropertyInfo 和 FieldInfo private static Dictionary<Type, Tuple<object, ComparePropertyFieldAttribute>[]> dict = new Dictionary<Type, Tuple<object, ComparePropertyFieldAttribute>[]>(); /// <summary> /// 只对带有ComparePropertyAttribute的属性和字段进行比较 /// </summary> /// <typeparam name="T"></typeparam> /// <param name="from"></param> /// <param name="to"></param> /// <param name="differenceMsg">不相同的字段或属性 的字符串说明</param> /// <returns>两者相同时, true; 两者不相同时, false</returns> public static bool CompareDifference<T>(T from, T to, out string differenceMsg) { var type = typeof(T); lock (dict) { if (!dict.ContainsKey(type)) { var list = new List<Tuple<object, ComparePropertyFieldAttribute>>(); // 获取带ComparePropertyAttribute的属性 var properties = type.GetProperties(); foreach (var property in properties) { var comparePropertyAttribute = (ComparePropertyFieldAttribute)property.GetCustomAttributes(typeof(ComparePropertyFieldAttribute), false).FirstOrDefault(); if (comparePropertyAttribute != null) { list.Add(Tuple.Create<object, ComparePropertyFieldAttribute>(property, comparePropertyAttribute)); } } // 获取带ComparePropertyAttribute字段 var fields = type.GetFields(); foreach (var field in fields) { var comparePropertyAttribute = (ComparePropertyFieldAttribute)field.GetCustomAttributes(typeof(ComparePropertyFieldAttribute), false).FirstOrDefault(); if (comparePropertyAttribute != null) { list.Add(Tuple.Create<object, ComparePropertyFieldAttribute>(field, comparePropertyAttribute)); } } dict.Add(type, list.ToArray()); } } var sb = new StringBuilder(200); //估计200字节能覆盖大多数情况了吧 var tupleArray = dict[type]; foreach (var tuple in tupleArray) { object v1 = null, v2 = null; if (tuple.Item1 is System.Reflection.PropertyInfo) { if (from != null) { v1 = ((System.Reflection.PropertyInfo)tuple.Item1).GetValue(from, null); } if (to != null) { v2 = ((System.Reflection.PropertyInfo)tuple.Item1).GetValue(to, null); } if (!object.Equals(v1, v2)) { sb.AppendFormat("{0}从 {1} 变成 {2}; ", tuple.Item2.PropertyName ?? ((System.Reflection.PropertyInfo)tuple.Item1).Name, v1 ?? "null", v2 ?? "null"); } } else if (tuple.Item1 is System.Reflection.FieldInfo) { if (from != null) { v1 = ((System.Reflection.FieldInfo)tuple.Item1).GetValue(from); } if (to != null) { v2 = ((System.Reflection.FieldInfo)tuple.Item1).GetValue(to); } if (!object.Equals(v1, v2)) { sb.AppendFormat("{0}从 {1} 变成 {2}; ", tuple.Item2.PropertyName ?? ((System.Reflection.FieldInfo)tuple.Item1).Name, v1 ?? "null", v2 ?? "null"); } } } differenceMsg = sb.ToString(); return differenceMsg == ""; } }
使用方法:
1. 将重要字段或属性加上 [ComparePropertyField] 特性, 目前只支持C#基本类型, 比如 int, bool, string等, 你自己写的class或者struct 需要重写 ToString()、Equals(), 按理说如果重写了Equals(), 那也需要重写GetHashCode(), 但确实没有用到GetHashCode(), 所以可以忽略Warning不重写GetHashCode()
2. 使用ComparePropertyFieldAttribute.CompareDifference 比较变更前后的实例即可
具体可参考下面的示例
![](https://images.cnblogs.com/OutliningIndicators/ExpandedBlockStart.gif)
class Program { static void Main(string[] args) { // 请用Debug测试, Release会优化掉一些代码导致测试不准确 System.Diagnostics.Stopwatch stopwatch = new Stopwatch(); var p1 = new Person() { INT = 1, BOOL = false, S = "p1", S2 = "p1" }; var p2 = new Person() { INT = 3, BOOL = false, S = "p1", S2 = "p1" }; string msg = null; stopwatch.Start(); for (int i = 0; i < 10000000; i++) { if (!p1.Equals(p2)) { msg = string.Format("{0} 变成 {1}", p1.ToString(), p2.ToString()); } } stopwatch.Stop(); Console.WriteLine("原生比较结果: " + msg); Console.WriteLine("原生比较耗时: " + stopwatch.Elapsed); stopwatch.Start(); for (int i = 0; i < 10000000; i++) { var result = ComparePropertyFieldAttribute.CompareDifference<Person>(p1, p2, out msg); } stopwatch.Stop(); Console.WriteLine("ComparePropertyAttribute比较结果: " + msg); Console.WriteLine("ComparePropertyAttribute比较: " + stopwatch.Elapsed); Console.ReadLine(); } } public class Person { [ComparePropertyField] public int INT { get; set; } [ComparePropertyFieldAttribute("布尔")] public bool BOOL { get; set; } [ComparePropertyFieldAttribute("字符串")] public string S { get; set; } [ComparePropertyFieldAttribute("S22222")] public string S2; public override bool Equals(object obj) { var another = obj as Person; if (another==null) { return false; } return this.INT == another.INT && this.BOOL == another.BOOL && this.S == another.S && this.S2 == another.S2; } public override string ToString() { return string.Format("i={0}, 布尔={1}, 字符串={2}, S22222={3}", INT, BOOL, S, S2); } }
耗时是原生的3倍, 考虑到只有记录日志才使用这个, 使用的机会很少, 对性能的损耗可以认为非常小.
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