C#中Action与delegate、EventHandler的差异

Action是一个泛型的委托，其内部即使用delegate去实现，当普通的delegate定义的参数与Action个数、类型一致时，两者实现的功能是一样的。只是Action的方式更加简洁、规范。如下：

        public delegate void DoDelegate(object parm);
        public DoDelegate DoMethod;

        public Action<object> doAction4OneParm;
        public Action<object, object> doAction4TwoParm;

        private void Form1_Load(object sender, EventArgs e)
        {
            DoMethod += DoTestMetohd;  //普通委托(由于委托定义时给定一个参数，故此处匹配一个参数的方法)
            doAction4OneParm += DoTestMetohd;  //Action委托(此处匹配一个参数的方法)
            doAction4TwoParm += DoTestMetohd;  //Action委托(此处匹配两个参数的方法)
        }

        private void DoTestMetohd(object parm)
        {
            MessageBox.Show(Convert.ToString(parm));
        }

        private void DoTestMetohd(object parm1, object parm2)
        {
            MessageBox.Show(Convert.ToString(parm1 + " " + parm2));
        }

而Action与delegate更重要的一个区别在于泛型，即Action的内部使用了泛型+委托，且泛型的方法的参数个数可扩展到16个，微软.net corefx中定义的Action内部代码如下：

namespace System
{
    [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Design", "CA1005:AvoidExcessiveParametersOnGenericTypes")]
    public delegate void Action<in T1, in T2, in T3, in T4, in T5, in T6, in T7, in T8, in T9>(T1 arg1, T2 arg2, T3 arg3, T4 arg4, T5 arg5, T6 arg6, T7 arg7, T8 arg8, T9 arg9);

    [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Design", "CA1005:AvoidExcessiveParametersOnGenericTypes")]
    public delegate void Action<in T1, in T2, in T3, in T4, in T5, in T6, in T7, in T8, in T9, in T10>(T1 arg1, T2 arg2, T3 arg3, T4 arg4, T5 arg5, T6 arg6, T7 arg7, T8 arg8, T9 arg9, T10 arg10);

    [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Design", "CA1005:AvoidExcessiveParametersOnGenericTypes")]
    public delegate void Action<in T1, in T2, in T3, in T4, in T5, in T6, in T7, in T8, in T9, in T10, in T11>(T1 arg1, T2 arg2, T3 arg3, T4 arg4, T5 arg5, T6 arg6, T7 arg7, T8 arg8, T9 arg9, T10 arg10, T11 arg11);

    [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Design", "CA1005:AvoidExcessiveParametersOnGenericTypes")]
    public delegate void Action<in T1, in T2, in T3, in T4, in T5, in T6, in T7, in T8, in T9, in T10, in T11, in T12>(T1 arg1, T2 arg2, T3 arg3, T4 arg4, T5 arg5, T6 arg6, T7 arg7, T8 arg8, T9 arg9, T10 arg10, T11 arg11, T12 arg12);

    [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Design", "CA1005:AvoidExcessiveParametersOnGenericTypes")]
    public delegate void Action<in T1, in T2, in T3, in T4, in T5, in T6, in T7, in T8, in T9, in T10, in T11, in T12, in T13>(T1 arg1, T2 arg2, T3 arg3, T4 arg4, T5 arg5, T6 arg6, T7 arg7, T8 arg8, T9 arg9, T10 arg10, T11 arg11, T12 arg12, T13 arg13);

    [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Design", "CA1005:AvoidExcessiveParametersOnGenericTypes")]
    public delegate void Action<in T1, in T2, in T3, in T4, in T5, in T6, in T7, in T8, in T9, in T10, in T11, in T12, in T13, in T14>(T1 arg1, T2 arg2, T3 arg3, T4 arg4, T5 arg5, T6 arg6, T7 arg7, T8 arg8, T9 arg9, T10 arg10, T11 arg11, T12 arg12, T13 arg13, T14 arg14);

    [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Design", "CA1005:AvoidExcessiveParametersOnGenericTypes")]
    public delegate void Action<in T1, in T2, in T3, in T4, in T5, in T6, in T7, in T8, in T9, in T10, in T11, in T12, in T13, in T14, in T15>(T1 arg1, T2 arg2, T3 arg3, T4 arg4, T5 arg5, T6 arg6, T7 arg7, T8 arg8, T9 arg9, T10 arg10, T11 arg11, T12 arg12, T13 arg13, T14 arg14, T15 arg15);

    [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Design", "CA1005:AvoidExcessiveParametersOnGenericTypes")]
    public delegate void Action<in T1, in T2, in T3, in T4, in T5, in T6, in T7, in T8, in T9, in T10, in T11, in T12, in T13, in T14, in T15, in T16>(T1 arg1, T2 arg2, T3 arg3, T4 arg4, T5 arg5, T6 arg6, T7 arg7, T8 arg8, T9 arg9, T10 arg10, T11 arg11, T12 arg12, T13 arg13, T14 arg14, T15 arg15, T16 arg16);
}

EventHandler是一个事件委托，即内部也采用委托来实现，但其更多的时候被定义成event，即事件的方式来使用。

以上纯个人在使用中的观点，欢迎指正批评!!!