关于比较对象,在"06判等对象是否相等"中大致可以总结为:

 

关于比较方法:
● 实例方法Equals(object obj)既可以比较值类型,也可以比较引用类型
● 静态方法Equals(object objA, object objB),比较值类型
● 静态方法ReferenceEquals(object objA, object objB),比较引用类型
● 比较引用类型可以用==,比较值类型不能用==

 

关于比较原则:
● 值类型比较的是值
● 引用类型比较的是引用地址

 

对于复杂类型,无论是复杂值类型(比如结构)还是复杂引用类型(包含值类型成员),经常要重写System.Object中的虚方法Equals(object obj)。比如,针对复杂值类型,可能这样重写:

public override bool Equals(object obj)
{
    if (obj == null)
    {
        return false;
    }
    RuntimeType type = (RuntimeType) base.GetType(); 
    RuntimeType type2 = (RuntimeType) obj.GetType();
    if (type2 != type) //比较两个对象是否是同一类型
    {
        return false;
    }
    object a = this;
    if (CanCompareBits(this)) //对象成员如果存在对于堆的引用返回false
    {
        return FastEqualsCheck(a, obj);
    }
    //反射获取值类型的所有字段
    FieldInfo[] fields = type.GetFields(BindingFlags.NonPublic | BindingFlags.Public | BindingFlags.Instance);
    for (int i = 0; i < fields.Length; i++) //遍历字段,对各个字段进行比较
    {
        object obj3 = ((RtFieldInfo) fields[i]).UnsafeGetValue(a);
        object obj4 = ((RtFieldInfo) fields[i]).UnsafeGetValue(obj);
        if (obj3 == null)
        {
            if (obj4 != null)
            {
                return false;
            }
        }
        else if (!obj3.Equals(obj4))
        {
            return false;
        }
    }
    return true;
}

.csharpcode, .csharpcode pre
{
font-size: small;
color: black;
font-family: consolas, "Courier New", courier, monospace;
background-color: #ffffff;
/*white-space: pre;*/
}
.csharpcode pre { margin: 0em; }
.csharpcode .rem { color: #008000; }
.csharpcode .kwrd { color: #0000ff; }
.csharpcode .str { color: #006080; }
.csharpcode .op { color: #0000c0; }
.csharpcode .preproc { color: #cc6633; }
.csharpcode .asp { background-color: #ffff00; }
.csharpcode .html { color: #800000; }
.csharpcode .attr { color: #ff0000; }
.csharpcode .alt
{
background-color: #f4f4f4;
width: 100%;
margin: 0em;
}
.csharpcode .lnum { color: #606060; }

 

而现在,在NuGet上输入"Compare .NET objects",可以获取到该组件,对任何.NET对象进行比较、列出各个属性的值甚至自定义比较规则。

 

  比较复杂类型:包含值类型成员

    public class Teacher
    {
        public int Id { get; set; }
        public string Name { get; set; }
        public DateTime JoinTime { get; set; }
        public TeacherClass TeacherClass { get; set; }
    }
 
    public enum TeacherClass
    {
        [Description("执教5年以上")]
        FirstClass = 0,
        [Description("执教3年以上")]
        SecondClass,
        [Description("执教1年以上")]
        ThirdClass
    }

 

主程序:

            Teacher teacher1 = new Teacher(){Id=1,JoinTime = new DateTime(2014,1,1),Name = "张老师",TeacherClass = TeacherClass.FirstClass};
            Teacher teacher2 = new Teacher() { Id = 2, JoinTime = new DateTime(2014, 1, 2), Name = "李老师", TeacherClass = TeacherClass.SecondClass };
 
            //获取Teacher属性的个数
            int propertyCount = typeof (Teacher).GetProperties().Length;
 
            //创建比较规则
            CompareLogic compareLogic = new CompareLogic()
            {
                Config = new ComparisonConfig()
                {
                    MaxDifferences = propertyCount//MaxDifferences的默认值是1
                } 
                
            };
 
            bool result = compareLogic.Compare(teacher1, teacher2).AreEqual;
            Console.Write(result);
            Console.ReadKey();    
 

.csharpcode, .csharpcode pre
{
font-size: small;
color: black;
font-family: consolas, "Courier New", courier, monospace;
background-color: #ffffff;
/*white-space: pre;*/
}
.csharpcode pre { margin: 0em; }
.csharpcode .rem { color: #008000; }
.csharpcode .kwrd { color: #0000ff; }
.csharpcode .str { color: #006080; }
.csharpcode .op { color: #0000c0; }
.csharpcode .preproc { color: #cc6633; }
.csharpcode .asp { background-color: #ffff00; }
.csharpcode .html { color: #800000; }
.csharpcode .attr { color: #ff0000; }
.csharpcode .alt
{
background-color: #f4f4f4;
width: 100%;
margin: 0em;
}
.csharpcode .lnum { color: #606060; }

结果:false

 

  比较复杂类型,并列出2个比较对象所有属性的值

            Teacher teacher1 = new Teacher(){Id=1,JoinTime = new DateTime(2014,1,1),Name = "张老师",TeacherClass = TeacherClass.FirstClass};
            Teacher teacher2 = new Teacher() { Id = 2, JoinTime = new DateTime(2014, 1, 2), Name = "李老师", TeacherClass = TeacherClass.SecondClass };
 
            //获取Teacher属性的个数
            int propertyCount = typeof (Teacher).GetProperties().Length;
 
            //创建比较规则
            CompareLogic compareLogic = new CompareLogic()
            {
                Config = new ComparisonConfig()
                {
                    MaxDifferences = propertyCount//MaxDifferences的默认值是1
                } 
                
            };
 
            //获取2个比较对象的不同之处
            List<Difference> differences = compareLogic.Compare(teacher1, teacher2).Differences;
 
            StringBuilder sb = new StringBuilder();
            foreach (Difference diff in differences)
            {
                sb.AppendLine("属性名称:" + diff.PropertyName);
                sb.AppendLine("第一个对象值:" + diff.Object1Value);
                sb.AppendLine("第二个对象值:" + diff.Object2Value + "\r\n");
            }
 
            using (StreamWriter outfile = new StreamWriter(@"F:\CompareObjects.txt"))
            {
                outfile.Write(sb.ToString());
            }
        }  

.csharpcode, .csharpcode pre
{
font-size: small;
color: black;
font-family: consolas, "Courier New", courier, monospace;
background-color: #ffffff;
/*white-space: pre;*/
}
.csharpcode pre { margin: 0em; }
.csharpcode .rem { color: #008000; }
.csharpcode .kwrd { color: #0000ff; }
.csharpcode .str { color: #006080; }
.csharpcode .op { color: #0000c0; }
.csharpcode .preproc { color: #cc6633; }
.csharpcode .asp { background-color: #ffff00; }
.csharpcode .html { color: #800000; }
.csharpcode .attr { color: #ff0000; }
.csharpcode .alt
{
background-color: #f4f4f4;
width: 100%;
margin: 0em;
}
.csharpcode .lnum { color: #606060; }

结果:

 

  比较复杂类型,并列出2个比较对象所有属性的值,对枚举属性自定义比较规则

需要一个自定义类,继承"Compare .NET objects"的BaseTypeComparer类,把打在枚举成员上的描述特性信息输出。

重写方法IsTypeMatch()用于判断2个比较对象的属性是否是枚举,如果是枚举,就采用重写方法CompareType()所定义的关于枚举属性的比较规则。

   public class CustomEnumComparer : BaseTypeComparer
    {
        public CustomEnumComparer() : base(RootComparerFactory.GetRootComparer()){}
 
        public override void CompareType(ComparisonResult result, object object1, object object2, string breadCrumb)
        {
            if (object1.ToString() != object2.ToString())
            {
                Difference difference = new Difference()
                {
                    PropertyName = breadCrumb,
                    Object1Value =  EnumHelper.GetDescription(object1),
                    Object2Value = EnumHelper.GetDescription(object2),
                    Object1 = new WeakReference(object1), //弱对象引用,即使被引用也可被垃圾回收
                    Object2 = new WeakReference(object2)
                };
                AddDifference(result,difference);
            }
        }
 
        public override bool IsTypeMatch(Type type1, Type type2)
        {
            return TypeHelper.IsEnum(type1) && TypeHelper.IsEnum(type2);
        }
    }
 
    //获取枚举类型的描述特性
    public static class EnumHelper
    {
        public static string GetDescription(object enumMember)
        {
            //获取枚举类型的字段信息
            FieldInfo fi = enumMember.GetType().GetField(enumMember.ToString());
 
            //获取字段上的描述特性
            IEnumerable<DescriptionAttribute> attributes = fi.GetCustomAttributes<DescriptionAttribute>(false);
            return attributes.Any() ? attributes.ElementAt(0).Description : enumMember.ToString();
        }
    }
 

.csharpcode, .csharpcode pre
{
font-size: small;
color: black;
font-family: consolas, "Courier New", courier, monospace;
background-color: #ffffff;
/*white-space: pre;*/
}
.csharpcode pre { margin: 0em; }
.csharpcode .rem { color: #008000; }
.csharpcode .kwrd { color: #0000ff; }
.csharpcode .str { color: #006080; }
.csharpcode .op { color: #0000c0; }
.csharpcode .preproc { color: #cc6633; }
.csharpcode .asp { background-color: #ffff00; }
.csharpcode .html { color: #800000; }
.csharpcode .attr { color: #ff0000; }
.csharpcode .alt
{
background-color: #f4f4f4;
width: 100%;
margin: 0em;
}
.csharpcode .lnum { color: #606060; }

 

只需要把针对枚举属性的自定义类赋值给CompareLogic实例即可:

            Teacher teacher1 = new Teacher(){Id=1,JoinTime = new DateTime(2014,1,1),Name = "张老师",TeacherClass = TeacherClass.FirstClass};
            Teacher teacher2 = new Teacher() { Id = 2, JoinTime = new DateTime(2014, 1, 2), Name = "李老师", TeacherClass = TeacherClass.SecondClass };
 
            //获取Teacher属性的个数
            int propertyCount = typeof (Teacher).GetProperties().Length;
 
            //创建比较规则
            CompareLogic compareLogic = new CompareLogic()
            {
                Config = new ComparisonConfig()
                {
                    MaxDifferences = propertyCount,//MaxDifferences的默认值是1
                    CustomComparers = new List<BaseTypeComparer>(){new CustomEnumComparer()}
                } 
                
            };
 
            //bool result = compareLogic.Compare(teacher1, teacher2).AreEqual;
            //Console.Write(result);
            //Console.ReadKey();
 
            //获取2个比较对象的不同之处
            List<Difference> differences = compareLogic.Compare(teacher1, teacher2).Differences;
 
            StringBuilder sb = new StringBuilder();
            foreach (Difference diff in differences)
            {
                sb.AppendLine("属性名称:" + diff.PropertyName);
                sb.AppendLine("第一个对象值:" + diff.Object1Value);
                sb.AppendLine("第二个对象值:" + diff.Object2Value + "\r\n");
            }
 
            using (StreamWriter outfile = new StreamWriter(@"F:\CompareObjects.txt"))
            {
                outfile.Write(sb.ToString());
            }

.csharpcode, .csharpcode pre
{
font-size: small;
color: black;
font-family: consolas, "Courier New", courier, monospace;
background-color: #ffffff;
/*white-space: pre;*/
}
.csharpcode pre { margin: 0em; }
.csharpcode .rem { color: #008000; }
.csharpcode .kwrd { color: #0000ff; }
.csharpcode .str { color: #006080; }
.csharpcode .op { color: #0000c0; }
.csharpcode .preproc { color: #cc6633; }
.csharpcode .asp { background-color: #ffff00; }
.csharpcode .html { color: #800000; }
.csharpcode .attr { color: #ff0000; }
.csharpcode .alt
{
background-color: #f4f4f4;
width: 100%;
margin: 0em;
}
.csharpcode .lnum { color: #606060; }

结果:

 

参考资料:

Compare .NET Objects Tutorial

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