class Program
    {
        static void Main(string[] args)
        {
            List<People> peoples = new List<People>
            {
                new  People{ ID=1,Name="xxx" },
                //new  People{ ID=1,Name="xxx" },
                new  People{ID=2,Name="yyy" },
            };

            peoples = peoples.Distinct(new Filter()).ToList();
    
            Console.WriteLine("Hello World!" + peoples.Count);
        }
    }
    
    public class Filter : IEqualityComparer<People>
    {
        public bool Equals([AllowNull] People x, [AllowNull] People y)
        {
            Console.WriteLine($"Equals->{x.ID},{y.ID}");
            return x.ID == y.ID;
        }

        public int GetHashCode([DisallowNull] People obj)
        {
            Console.WriteLine($"GetHashCode->{obj.ID}");
            return obj.ID;
        }
    }
 

IEqualityComparer 比較規則:

1. 如果 HashCode 不同，則不執行 Equals ， 直接判定為不同
2. 如果 HashCode 相同，則執行 Equals ， 根據 Equals 判定相不相不同