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C#在System命名空间下提供两个委托Action和Func，这两个委托最多提供16个参数，基本上可以满足所有自定义事件所需的委托类型。几乎所有的 事件 都可以使用这两个内置的委托Action和Func进行处理。

Action委托：

Action定义提供0~16个参数，无返回值的委托

共有17种重载：

public delegate void Action();

public delegate void Action<in T>(T obj);

public delegate void Action<in T1, in T2>(T1 arg1, T2 arg2);

public delegate void Action<in T1, in T2, in T3>(T1 arg1, T2 arg2, T3 arg3);

。。。。。。

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);

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);

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);

Func委托：

Func定义提供0~16个参数，有返回类型的委托

共有17种重载：

public delegate TResult Func<out TResult>();

public delegate TResult Func<in T, out TResult>(T arg);

public delegate TResult Func<in T1, in T2, out TResult>(T1 arg1, T2 arg2);

public delegate TResult Func<in T1, in T2, in T3, out TResult>(T1 arg1, T2 arg2, T3 arg3);

。。。。。。

public delegate TResult Func<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, out TResult>(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);

public delegate TResult Func<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, out TResult>(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);

public delegate TResult Func<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, out TResult>(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);

Action、Func委托与常见委托的类比

线程开始委托

public delegate void ThreadStart();

System.Threading.ThreadStart 委托 类似于 Action

事件处理委托

public delegate void EventHandler(object sender, EventArgs e);

EventHandler 委托 类似于 Action<object,EventArgs>

判定委托

public delegate bool Predicate<in T>(T obj);

Predicate<T> 委托 类似于 Func<T,bool>

比较委托

public delegate int Comparison<in T>(T x, T y);

Comparison<T> 委托 类似于 Func<T, T, int>

测试程序：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;namespace IntegratedDelegateDemo
{class Program{static void Main(string[] args){//Action定义无返回值的委托，最多有16个参数//Func定义一个有返回值的委托，最多有16个参数Predicate<int> predicate = x => x > 0;Func<int, bool> func = new Func<int, bool>(predicate);Comparison<double> comparison = (x, y) => x - y > 0 ? 1 : 0;int num = -8;bool isPositive = func(num);Console.WriteLine($"【{num}】是否为正数:【{isPositive}】");Func<double, double, int> funcComparion = new Func<double, double, int>(comparison);double xNumber = 7.666;double yNumber = 6.55;Console.WriteLine($"两个数字进行比较【{xNumber}】>【{yNumber}】的结果为【{funcComparion(xNumber, yNumber)}】");List<string> gjqtList = new List<string>() { "百里屠苏", "风晴雪", "红玉", "方兰生" };gjqtList.ForEach(role => Console.WriteLine(role));Action action = () => Console.WriteLine("测试无参数，无返回值委托");System.Threading.ThreadStart threadStart = new System.Threading.ThreadStart(action);threadStart.Invoke();Func<short, short, int> funcComparison = (x, y) => y - x;Comparison<short> comparisonDesc = new Comparison<short>(funcComparison);short[] testSortArray = new short[] { 50, 25, 43, 69, 16, 14, 22 };Console.WriteLine($"使用委托进行逆序排序，原数组为【{string.Join(",", testSortArray)}】");Array.Sort(testSortArray, comparisonDesc);Console.WriteLine($"逆序排序已结束，逆序排序后的数组为【{string.Join(",", testSortArray)}】");Console.ReadLine();}}
}

运行截图：