时间：2021-01-02 15:11:29 | 栏目：.NET代码 | 点击：次
Equals和GetHashCode
Equals每个实现都必须遵循以下约定:
GetHashCode:
IEqualityComparer实现
下面我们创建一个学生类,从而进一步的实现我们对象数据的对比
public class Student
{
public string Name { get; set; }
public int Age { get; set; }
}
通过如下代码我们将通过distinct方法实现我们的过滤.
class Program
{
static void Main(string[] args)
{
List<Student> students = new List<Student>
{
new Student{ Name = "MR.A", Age = 32},
new Student{ Name = "MR.B", Age = 34},
new Student{ Name = "MR.A", Age = 32}
};
Console.WriteLine("distinctStudents has Count = {0}", students.Distinct().Count());//distinctStudents has Count = 3
Console.ReadLine();
}
}
我们需要达到的是忽略相同数据的对象,但是并没有达到我们如期的效果.因为是distinct默认比较的是对象的引用...所以这样达不到我们预期效果.那我们修改一下来实现我们预期效果.
在默认情况下Equals具有以下行为:
Distinct(IEnumerable, IEqualityComparer)
通过使用指定的 IEqualityComparer 对值进行比较，返回序列中的非重复元素.
类型参数
参数
返回
一个包含源序列中的非重复元素的 IEnumerable。
我们来看如下代码片段
public class StudentComparator : EqualityComparer<Student>
{
public override bool Equals(Student x,Student y)
{
return x.Name == y.Name && x.Age == y.Age;
}
public override int GetHashCode(Student obj)
{
return obj.Name.GetHashCode() * obj.Age;
}
}
上述代码片段如果两个Equals返回的true并且GetHashCode返回相同的哈希码,则认为两个对象相等.
重写Equals和GetHashCode
var stu1 = new Student { Name = "MR.A", Age = 32 };
var stu2 = new Student { Name = "MR.A", Age = 32 };
bool result = stu1.Equals(stu2); //false because it's reference Equals
上述代码片段执行后结果非预期效果.我们将进一步的去实现代码,以达到预期效果....
public class Student
{
public string Name { get; set; }
public int Age { get; set; }
public override bool Equals(object obj)
{
var stu = obj as Student;
if (stu == null) return false;
return Name == stu.Name && Age == stu.Age;
}
public override int GetHashCode()
{
return Name.GetHashCode() * Age;
}
}
var stu1 = new Student { Name = "MR.A", Age = 32 };
var stu2 = new Student { Name = "MR.A", Age = 32 };
bool result = stu1.Equals(stu2); //result is true
我们再使用LINQ Distinct方法进行过滤和查询,同时将会检查Equals和GetHashCode
List<Student> students = new List<Student>
{
new Student{ Name = "MR.A", Age = 32},
new Student{ Name = "MR.B", Age = 34},
new Student{ Name = "MR.A", Age = 32}
};
Console.WriteLine("distinctStudents has Count = {0}", students.Distinct().Count()); //distinctStudents has Count = 2
作者：@冯辉
出处：https://www.cnblogs.com/yyfh/p/12245916.html?utm_source=tuicool&utm_medium=referral