c# 反射用法及效率对比

反射实例化类

public class Person
{
  public string Name { get; set; }

  public Person(string name)
  {
    this.Name = name;
  }

  public string Say(string msg)
  {
    return $"{Name}: {msg}";
  }
}

class Program
{
  // 测试次数
  const int count = 10000000;

  static void Main(string[] args)
  {
    CreateInstance0();
    CreateInstance1();
    CreateInstance2();
    CreateInstance3();
    CreateInstance4();

    Console.Read();
  }

  static void CreateInstance0()
  {
    Stopwatch watch = new Stopwatch();
    watch.Start();

    for (var i = 0; i < count; i++)
    {
      Person person = new Person("张三");
    }

    watch.Stop();
    Console.WriteLine($"{watch.Elapsed} - new");
  }

  static void CreateInstance1()
  {
    Stopwatch watch = new Stopwatch();
    watch.Start();

    for (var i = 0; i < count; i++)
    {
      object person = Activator.CreateInstance(typeof(Person), "张三");
    }

    watch.Stop();
    Console.WriteLine($"{watch.Elapsed} - Activator.CreateInstance");
  }

  static void CreateInstance2()
  {
    Assembly assembly = Assembly.GetExecutingAssembly();

    Stopwatch watch = new Stopwatch();
    watch.Start();

    for (var i = 0; i < count; i++)
    {
      Person obj = (Person)assembly.CreateInstance("ConsoleTest.Person", true, BindingFlags.Default, null, new object[] { "张三" }, null, null);
    }

    watch.Stop();
    Console.WriteLine($"{watch.Elapsed} - Assembly.CreateInstance");
  }

  static void CreateInstance3()
  {
    Assembly assembly = Assembly.GetExecutingAssembly();

    Stopwatch watch = new Stopwatch();
    watch.Start();

    for (var i = 0; i < count; i++)
    {
      Type type = assembly.GetType("ConsoleTest.Person");
      object person = Activator.CreateInstance(type, "张三");
    }
    watch.Stop();
    Console.WriteLine($"{watch.Elapsed} - Assembly.CreateInstance1");
  }

  static void CreateInstance4()
  {
    Assembly assembly = Assembly.GetExecutingAssembly();

    Stopwatch watch = new Stopwatch();
    watch.Start();

    Type type = assembly.GetType("ConsoleTest.Person");
    for (var i = 0; i < count; i++)
    {
      object person = Activator.CreateInstance(type, "张三");
    }
    watch.Stop();
    Console.WriteLine($"{watch.Elapsed} - Assembly.CreateInstance2");
  }
}

• 通过反射实例化对象，要比直接 new 要慢 50 倍左右
• assembly.CreateInstance 要比 Activator.CreateInstance 慢，主要的性能损耗在 Assembly.GetType

反射调用类的方法

class Program
{
  // 测试次数
  const int count = 10000000;

  static void Main(string[] args)
  {
    InvokeMethod0();
    InvokeMethod1();
    InvokeMethod2();
    InvokeMethod3();
    InvokeMethod4();

    Console.Read();
  }

  static void InvokeMethod0()
  {
    Person person = new Person("张三");

    Stopwatch watch = new Stopwatch();
    watch.Start();

    for (var i = 0; i < count; i++)
    {
      string name = person.Say("Hello World!");
    }

    watch.Stop();
    Console.WriteLine($"{watch.Elapsed} - 直接调用");
  }

  static void InvokeMethod1()
  {
    Person person = (Person)Activator.CreateInstance(typeof(Person), "张三");

    Stopwatch watch = new Stopwatch();
    watch.Start();

    for (var i = 0; i < count; i++)
    {
      string name = person.Say("Hello World!");
    }

    watch.Stop();
    Console.WriteLine($"{watch.Elapsed} - 反射缓存类调用");
  }

  static void InvokeMethod2()
  {
    Person person = (Person)Activator.CreateInstance(typeof(Person), "张三");
    MethodInfo method = typeof(Person).GetMethod(nameof(Person.Say), new Type[] { typeof(string) });
    Func func = (Func)method.CreateDelegate(typeof(Func), person);

    Stopwatch watch = new Stopwatch();
    watch.Start();

    for (var i = 0; i < count; i++)
    {
      string result = func("Hello World!");
    }

    watch.Stop();
    Console.WriteLine($"{watch.Elapsed} - 使用反射创建出来的委托调用");
  }

  static void InvokeMethod3()
  {
    Person person = (Person)Activator.CreateInstance(typeof(Person), "张三");

    MethodInfo method = typeof(Person).GetMethod(nameof(Person.Say), new Type[] { typeof(string) });

    object[] parameters = new object[] { "Hello World!" };

    Stopwatch watch = new Stopwatch();
    watch.Start();

    for (var i = 0; i < count; i++)
    {
      string name = (string)method.Invoke(person, parameters);
    }

    watch.Stop();
    Console.WriteLine($"{watch.Elapsed} - 使用反射得到的方法缓存调用");
  }

  static void InvokeMethod4()
  {
    Person person = (Person)Activator.CreateInstance(typeof(Person), "张三");

    object[] parameters = new object[] { "Hello World!" };

    Stopwatch watch = new Stopwatch();
    watch.Start();

    for (var i = 0; i < count; i++)
    {
      string result = (string)(typeof(Person).GetMethod(nameof(Person.Say))?.Invoke(person, parameters));
    }

    watch.Stop();
    Console.WriteLine($"{watch.Elapsed} - 直接使用反射调用");
  }
}

• 反射得到实例后调用方法和直接调用方法效率一样
• 缓存反射方法调用和直接使用反射调用都非常耗效率

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