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

/// <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(); //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 == "";

    }

}

ComparePropertyFieldAttribute

　　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

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 = , BOOL = false, S = "p1", S2 = "p1" };

        var p2 = new Person() { INT = , BOOL = false, S = "p1", S2 = "p1" };

        string msg = null;

        stopwatch.Start();

        for (int i = ; i < ; 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 = ; i < ; 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.

　　end

巴特西

C#使用反射获取对象变化的情况

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