c# - 如何在 C# 中合并 Multicast Delegates 返回的结果？

Question

我想通过调用多播委托(delegate)来组合两个函数调用返回的结果。但是我不断收到一个异常，说 del 是一个变量，但像方法一样使用。

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace MultiDelegateConsoleApplication
{
    public delegate void SampleMultiDelegate(string args,out string SampleString);

    class Program
    {
        public static void SayHello(string args,out string s1)
        {
            s1 = "Hello " + args;
        }
        public static void SayGoodbye(string args,out string s2)
        {
            s2 = "Goodbye " + args;
        }

        static void Main(string[] args)
        {
            SampleMultiDelegate sampleMultiDelegate = new SampleMultiDelegate(SayHello);
            sampleMultiDelegate += SayGoodbye;
            string param1 = "Chiranjib";
            string param2,param3;
            Console.WriteLine("**************Individual Function Invoke***********");
            SayHello(param1,out param2);
            SayGoodbye(param1, out param3);
            Console.WriteLine("**************Multicast Delegate Invoke***********");
            sampleMultiDelegate(param1,out param2);
            Console.WriteLine(param2); //The multicast delegate will always return the result of the last function
            string result;
            foreach (Delegate del in sampleMultiDelegate.GetInvocationList())
            {
                result = del(param1,out param2);
            }

            Console.ReadKey();
            Console.ReadLine();
        }
    }
}

你能解释一下并帮助我修复错误吗？

Answer 1

您需要将调用列表中的每个函数都转换为委托(delegate)类型才能使用正常的函数调用语法:

void Main()
{
    var sampleMultiDelegate = new SampleMultiDelegate(SayHello);
    sampleMultiDelegate += SayGoodbye;
    var param1 = "Chiranjib";
    string param2;
    string result = "";
    foreach (var del in sampleMultiDelegate.GetInvocationList())
    {
        var f = (SampleMultiDelegate)del;
        f(param1, out param2);
        result += param2 + "\r\n";
    }

    Console.WriteLine(result);
}

还修复了这样一个事实，即您的委托(delegate)调用在返回 void 时不会有任何结果。