測試

新建一個Person類

public class Person
  {
    public Person(string name,int id)
    {
      Name = name;
      Id = id;
    }
    public string Name { get; set; }
    public int Id { get; set; }

  }

初始化List 中有一百萬條資料，然後分別通過每種方法判斷xiaoming是否在List中，程式碼如下

static void Main(string[] args)
    {
      List<Person> persons = new List<Person>();
      //初始化persons資料
      for (int i = 0; i < 1000000; i++)
      {
        Person person = new Person("My" + i,i);
        persons.Add(person);
      }
      Person xiaoming=new Person("My999999",999999);
      
      //下面通過三種方法判斷persons中是否包含xiaoming
      Stopwatch watch = new Stopwatch();
      watch.Start();
      bool a = persons.Contains(xiaoming);
      watch.Stop();

      Stopwatch watch1 = new Stopwatch();
      watch1.Start();
      bool b = persons.Exists(x=>x.Id==xiaoming.Id);
      watch1.Stop();

      Stopwatch watch2 = new Stopwatch();
      watch2.Start();
      bool c = persons.Where(x=>x.Id==xiaoming.Id).Any();
      watch2.Stop();

      Stopwatch watch3 = new Stopwatch();
      watch3.Start();
      bool d = persons.Any(x => x.Id == xiaoming.Id);
      watch3.Stop();

      Console.WriteLine("Contains耗時：" + watch.Elapsed.TotalMilliseconds);
      Console.WriteLine("Exists耗時：" + watch1.Elapsed.TotalMilliseconds);
      Console.WriteLine("Where耗時：" + watch2.Elapsed.TotalMilliseconds);
      Console.WriteLine("Any耗時：" + watch3.Elapsed.TotalMilliseconds);
      Console.ReadLine();
    }

執行結果如下圖所示

結論

通過上圖可以看出效能排序為

Contains > Exists > Where > Any

注意：
Contains中不能帶查詢條件

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