C#例項化物件的三種方式及效能對比

前言

做專案過程中有個需求要例項化兩萬個物件並新增到List中，這個過程大概需要1min才能載入完（傳參較多），於是開啟了程式碼優化之旅，再此記錄。
首先想到的是可能例項化比較耗時，於是開始對每種例項化方式進行測試，過程如下

例項化方式

1、用 New 關鍵字例項化一個類
2、用 Activator 例項化一個類
3、用 Assembly 例項化一個類

程式碼實現

測試環境：
vs2019 .NET Framework 4.7
Intel Core i7-10510U CPU

首先定義一個類Person

public class Person 
{  
    public Person()
    {
    }
    public Person(string name)
    {
        Name = name;
    }
    public string Name { get; set; }
}

我們先在無參的建構函式中例項化，每種方式進行十次，每次例項化十萬次，程式碼如下

static void Main(string[] args)
        {
            Console.WriteLine("例項化物件的耗時比較（單位：毫秒）");
            Console.Write("                    ");
            for (int i = 1; i <= 10; i++)
                Console.Write("{0:G}", i.ToString().PadLeft(5));
            Console.Write("\n");
            Console.Write("InstanceByNew".PadRight(20));
            for (int i = 1; i <= 10; i++)
            {
                Person person = null;
                Stopwatch watch = new Stopwatch();
                watch.Start();
                for (int j = 0; j < 100000; j++)
                    person = new Person();
                watch.Stop();
                Console.Write(watch.ElapsedMilliseconds.ToString().PadLeft(5));
            }
            Console.Write("\n");
            Console.Write("InstanceByActivator".PadRight(20));
            for (int i = 1; i <= 10; i++)
            {
                Type type = Type.GetType("ConsoleApp1.Person");
                Person person = null;

                Stopwatch watch = new Stopwatch();
                watch.Start();
                for (int j = 0; j < 100000; j++)
                {
                    object obj = Activator.CreateInstance(type);
                    person = obj as Person;
                }
                watch.Stop();
                Console.Write(watch.ElapsedMilliseconds.ToString().PadLeft(5));
            }
            Console.Write("\n");
            Console.Write("InstanceByAssembly".PadRight(20));
            for (int i = 1; i <= 10; i++)
            {
                Assembly assembly = Assembly.Load("InstancePerformance");
                Person person = null;

                Stopwatch watch = new Stopwatch();
                watch.Start();
                for (int j = 0; j < 100000; j++)
                {
                    object obj = assembly.CreateInstance("ConsoleApp1.Person");
                    person = obj as Person;
                }
                watch.Stop();
                Console.Write(watch.ElapsedMilliseconds.ToString().PadLeft(5));
            }
            Console.Write("\n");
            Console.ReadKey();
        }

執行結果如下：

然後來看下有參建構函式中例項化的程式碼和結果

static void Main(string[] args)
        {
            Console.WriteLine("例項化物件的耗時比較（單位：毫秒）");
            Console.Write("                    ");
            for (int i = 1; i <= 10; i++)
                Console.Write("{0:G}", i.ToString().PadLeft(5));
            Console.Write("\n");
            Console.Write("InstanceByNew".PadRight(20));
            for (int i = 1; i <= 10; i++)
            {
                Person person = null;
                Stopwatch watch = new Stopwatch();
                watch.Start();
                for (int j = 0; j < 100000; j++)
                    person = new Person("Test"+j);
                watch.Stop();
                Console.Write(watch.ElapsedMilliseconds.ToString().PadLeft(5));
            }
            Console.Write("\n");
            Console.Write("InstanceByActivator".PadRight(20));
            for (int i = 1; i <= 10; i++)
            {
                Type type = Type.GetType("ConsoleApp1.Person");
                Person person = null;

                Stopwatch watch = new Stopwatch();
                watch.Start();
                for (int j = 0; j < 100000; j++)
                {
                    object obj = Activator.CreateInstance(type,new object[]{"Test"+j});
                    person = obj as Person;
                }
                watch.Stop();
                Console.Write(watch.ElapsedMilliseconds.ToString().PadLeft(5));
            }
            Console.Write("\n");
            Console.Write("InstanceByAssembly".PadRight(20));
            for (int i = 1; i <= 10; i++)
            {
                Assembly assembly = Assembly.Load("InstancePerformance");
                Person person = null;

                Stopwatch watch = new Stopwatch();
                watch.Start();
                for (int j = 0; j < 100000; j++)
                {
                    object obj = assembly.CreateInstance("ConsoleApp1.Person", true, System.Reflection.BindingFlags.Default, null, new []{"Test"+j}, null, null);
                    person = obj as Person;
                }
                watch.Stop();
                Console.Write(watch.ElapsedMilliseconds.ToString().PadLeft(5));
            }
            Console.Write("\n");
            Console.ReadKey();
        }

執行結果如下：

結論

從上面的執行結果可以看出這三種方式的效能排序為
New > Activator > Assembly
但使用哪種方法還要視情況而定

後續

以上可以看出New效能最高，而我就是使用的New，問題還沒解決，把問題指向判斷List是否存在某元素上，於是開始測試List中的Contains, Exists, Any，Where。詳情請點選.