C#中对集合排序的三种方式

对集合排序，可能最先想到的是使用OrderBy方法。

    class Program
    {
        static void Main(string[] args)
        {
            IEnumerable<Student> result = GetStudents().OrderBy(r => r.Score);
            foreach (var item in result)
            {
                Console.WriteLine(item.Name + "--" + item.Score);
            }
            Console.ReadKey();
        }
        private static List<Student> GetStudents()
        {
            return new List<Student>()
            {
                new Student(){Id = 1, Name = "张三",Age = 15, Score = 80},
                new Student(){Id = 2, Name = "李四",Age = 16, Score = 70},
                new Student(){Id = 3, Name = "赵武",Age = 14, Score = 90}
            };
        }
    }
    public class Student 
    {
        public int Id { get; set; }
        public string Name { get; set; }
        public int Age { get; set; }
        public int Score { get; set; }
    }

以上，OrderBy返回的类型是IEnumerable<Student>。

如果想使用List<T>的Sort方法，就需要让Student实现IComparable<Student>接口。

   class Program
    {
        static void Main(string[] args)
        {
            List<Student> result = GetStudents();
            result.Sort();
            foreach (var item in result)
            {
                Console.WriteLine(item.Name + "--" + item.Score);
            }
            Console.ReadKey();
        }
        private static List<Student> GetStudents()
        {
            return new List<Student>()
            {
                new Student(){Id = 1, Name = "张三",Age = 15, Score = 80},
                new Student(){Id = 2, Name = "李四",Age = 16, Score = 70},
                new Student(){Id = 3, Name = "赵武",Age = 14, Score = 90}
            };
        }
    }
    public class Student : IComparable<Student>
    {
        public int Id { get; set; }
        public string Name { get; set; }
        public int Age { get; set; }
        public int Score { get; set; }
        
        public int CompareTo(Student other)
        {
          return  this.Score.CompareTo(other.Score);
        }
    }

让Student实现IComparable<Student>接口固然很好，如果Student是一个密封类，我们无法让其实现IComparable<Student>接口呢？不用担心，Sort方法提供了一个重载，可以接收IComparer接口类型。

   class Program
    {
        static void Main(string[] args)
        {
            List<Student> result = GetStudents();
            result.Sort(new StudentSorter());
            foreach (var item in result)
            {
                Console.WriteLine(item.Name + "--" + item.Score);
            }
            Console.ReadKey();
        }
        private static List<Student> GetStudents()
        {
            return new List<Student>()
            {
                new Student(){Id = 1, Name = "张三",Age = 15, Score = 80},
                new Student(){Id = 2, Name = "李四",Age = 16, Score = 70},
                new Student(){Id = 3, Name = "赵武",Age = 14, Score = 90}
            };
        }
    }
    public class Student
    {
        public int Id { get; set; }
        public string Name { get; set; }
        public int Age { get; set; }
        public int Score { get; set; }
    }
    public class StudentSorter : IComparer<Student>
    {
        public int Compare(Student x, Student y)
        {
            return x.Score.CompareTo(y.Score);
        }
    }

综上，如果我们想对一个集合排序，大致有三种方式：

1、使用OrderBy方法，返回IEnumerable<T>类型。
2、让集合元素实现IComparable<T>接口，再使用Sort方法，返回void。
3、集合元素不实现IComparable<T>接口，针对集合元素类型写一个实现IComparer<T>接口的类，把该类实例作为Sort方法的参数。

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