c# .ｎｅｔ３．５实现异步编程 实例

以下是一个使用.NET Framework 3.5实现异步编程的示例：

using System;
using System.Threading;

class Program
{
    static void Main(string[] args)
    {
        Console.WriteLine("Main thread started.");

        // 使用委托和回调函数实现异步编程
        Console.WriteLine("Using delegate and callback to implement asynchronous programming.");
        MyDelegate myDelegate = new MyDelegate(DoSomething);
        myDelegate.BeginInvoke(5000, new AsyncCallback(Callback), null);

        // 使用线程池实现异步编程
        Console.WriteLine("Using thread pool to implement asynchronous programming.");
        ThreadPool.QueueUserWorkItem(new WaitCallback(DoSomethingThreadPool), 3000);

        // 使用异步方法实现异步编程
        Console.WriteLine("Using async method to implement asynchronous programming.");
        DoSomethingAsync(2000);

        Console.WriteLine("Main thread ended.");
        Console.ReadLine();
    }

    // 定义委托和回调函数
    public delegate void MyDelegate(int milliseconds);
    public static void DoSomething(int milliseconds)
    {
        Console.WriteLine("DoSomething started.");
        Thread.Sleep(milliseconds);
        Console.WriteLine("DoSomething completed.");
    }
    public static void Callback(IAsyncResult ar)
    {
        Console.WriteLine("Callback started.");
        MyDelegate myDelegate = (MyDelegate)ar.AsyncState;
        myDelegate.EndInvoke(ar);
        Console.WriteLine("Callback completed.");
    }

    // 使用线程池
    public static void DoSomethingThreadPool(object state)
    {
        Console.WriteLine("DoSomethingThreadPool started.");
        int milliseconds = (int)state;
        Thread.Sleep(milliseconds);
        Console.WriteLine("DoSomethingThreadPool completed.");
    }

    // 使用异步方法
    public static async void DoSomethingAsync(int milliseconds)
    {
        Console.WriteLine("DoSomethingAsync started.");
        await Task.Run(() => Thread.Sleep(milliseconds));
        Console.WriteLine("DoSomethingAsync completed.");
    }
}

该示例使用了三种不同的方法来实现异步编程：使用委托和回调函数、使用线程池、使用异步方法。在每种方法中，都使用Thread.Sleep方法模拟耗时操作。注意，在使用异步方法时，需要使用async和await关键字来标记异步方法和等待异步操作完成。