【C#】反射的用法及效率對比

反射例項化類

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
{
    // 測試次數
    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("張三");
        }

        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), "張三");
        }

        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[] { "張三" }, 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, "張三");
        }
        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, "張三");
        }
        watch.Stop();
        Console.WriteLine($"{watch.Elapsed} - Assembly.CreateInstance2");
    }
}

• 通過反射例項化物件，要比直接 new 要慢 50 倍左右
• assembly.CreateInstance 要比 Activator.CreateInstance 慢，主要的效能損耗在 Assembly.GetType

反射呼叫類的方法

class Program
{
    // 測試次數
    const int count = 10000000;

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

        Console.Read();
    }

    static void InvokeMethod0()
    {
        Person person = new Person("張三");

        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} - 直接呼叫");
    }

    static void InvokeMethod1()
    {
        Person person = (Person)Activator.CreateInstance(typeof(Person), "張三");

        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} - 反射快取類呼叫");
    }

    static void InvokeMethod2()
    {
        Person person = (Person)Activator.CreateInstance(typeof(Person), "張三");
        MethodInfo method = typeof(Person).GetMethod(nameof(Person.Say), new Type[] { typeof(string) });
        Func<string, string> func = (Func<string, string>)method.CreateDelegate(typeof(Func<string, string>), 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} - 使用反射建立出來的委託呼叫");
    }

    static void InvokeMethod3()
    {
        Person person = (Person)Activator.CreateInstance(typeof(Person), "張三");

        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快取呼叫");
    }

    static void InvokeMethod4()
    {
        Person person = (Person)Activator.CreateInstance(typeof(Person), "張三");

        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} - 直接使用反射呼叫");
    }
}

• 反射得到例項後呼叫方法和直接呼叫方法效率一樣
• 快取反射方法呼叫和直接使用反射呼叫都非常耗效率