C# event Action＜＞ & event EventHandler＜＞

event作用

我们可以通过对event的使用完成回调功能。本节通过简单的例子引入Action和EventHandler。

EventHandler

    class Program
    {
        private static event EventHandler<DiagnosticsArgs> DiagnosticsEvent;
        static void Main(string[] args)
        {
            DiagnosticsEvent += Program_DiagnosticsEvent;//注册回调函数
            for (int i = 0; i < 10; i++)
            {
                if (i == 5)
                {
                    DiagnosticsEvent?.Invoke(null, new DiagnosticsArgs(100, false));//唤醒回调函数Program_DiagnosticsEvent
                }
                Thread.Sleep(500);
            }
        }

        /// <summary>
        /// 回调函数本身
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        private static void Program_DiagnosticsEvent(object sender, DiagnosticsArgs e)
        {
            Console.WriteLine(e.FirstParamater + "\n" + e.SecondParameter);
        }
    }

    internal class DiagnosticsArgs : EventArgs
    {
        private int _firstParamater;

        public int FirstParamater
        {
            get { return _firstParamater; }
            set { _firstParamater = value; }
        }

        private bool _secondParameter;

        public bool SecondParameter
        {
            get { return _secondParameter; }
            set { _secondParameter = value; }
        }


        public DiagnosticsArgs(int first, bool second)
        {
            FirstParamater = first;
            SecondParameter = second;
        }
    }

结果：

Action

    class Program
    {
        //private static event EventHandler<DiagnosticsArgs> DiagnosticsEvent;
        private static event Action<DiagnosticsArgs> DiagnosticsEvent;
        static void Main(string[] args)
        {
            DiagnosticsEvent += Program_DiagnosticsEvent;//注册回调函数
            for (int i = 0; i < 10; i++)
            {
                if (i == 5)
                {
                    //DiagnosticsEvent?.Invoke(null, new DiagnosticsArgs(100, false));//唤醒回调函数Program_DiagnosticsEvent
                    DiagnosticsEvent?.Invoke(new DiagnosticsArgs(100, false));//唤醒回调函数Program_DiagnosticsEvent
                }
                Thread.Sleep(500);
            }
        }

        private static void Program_DiagnosticsEvent(DiagnosticsArgs e)
        {
            Console.WriteLine(e.FirstParamater + "\n" + e.SecondParameter);
        }

        /// <summary>
        /// 回调函数本身
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        //private static void Program_DiagnosticsEvent(object sender, DiagnosticsArgs e)
        //{
        //    Console.WriteLine(e.FirstParamater + "\n" + e.SecondParameter);
        //}
    }

    internal class DiagnosticsArgs : EventArgs
    {
        private int _firstParamater;

        public int FirstParamater
        {
            get { return _firstParamater; }
            set { _firstParamater = value; }
        }

        private bool _secondParameter;

        public bool SecondParameter
        {
            get { return _secondParameter; }
            set { _secondParameter = value; }
        }


        public DiagnosticsArgs(int first, bool second)
        {
            FirstParamater = first;
            SecondParameter = second;
        }
    }

运行结果和上一次相同。

结论

单从功能上来讲，二者都可以实现函数回调，但是从设计模式的角度来看，EventHandler的封装性似乎更好，具体可参考StackOverflow相关讨论。