开始和结束异步操作(xxx表示同步方法的名词):Beginxxx和Endxxx

例如:FileStream类的对象的BeginRead()和EndRead()

BeginRead()方法返回一个IAsyncResult对象,表示异步操作的状态。如果喜欢阻塞当前线程并等待读取完成,那么可以调用EndRead()方法,并将IAsyncResult对象作为参数传递给该方法。

BeginRead()方法实际就是启动一个新线程来进行异步读取,而EndRead()方法相当与调用了异步线程的Join方法。

demo1:创建10个异步线程,每个线程负责读取10个字节到缓冲区中,而回调方法GetPosition在每个线程结束后都会被调用

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

using System.IO;

namespace AsyncCallback
{
class Program
{
static void Main(string[] args)
{
using (FileStream fs = new FileStream(@"F:\123.txt", FileMode.Open, FileAccess.Read))
{
byte[] bs = new byte[1000];
for (int i = 0; i < 10; i++)
{
fs.BeginRead(bs, i * 100, 100, GetPosition, fs);
}
StringBuilder sb = new StringBuilder();
for (int i = 0; i < 100; i++)
{
sb.Append((char)i);
}
Console.ReadKey();
}

    }    static void GetPosition(IAsyncResult iar)    {        FileStream fs = (FileStream)iar.AsyncState;        Console.WriteLine("本次读取文件文职:{0}",fs.Position);        fs.EndRead(iar);    }}

}
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demo2:delegate委托的BeginInvoke、EndInvoke、AsyncCallback用法

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

using System.Threading;

namespace BeginInvoke
{
class Program
{
static void Main(string[] args)
{
NewTaskDelegate task = NewTask;
//int n = task(2000);

        //AsyncCallback方法一        //AsyncCallback callback = new AsyncCallback(MyAsyncCallback);        //IAsyncResult asyncResult = task.BeginInvoke(2000, callback, task);        //AsyncCallback方法二        IAsyncResult asyncResult = task.BeginInvoke(2000, MyAsyncCallback, task);        //int result = task.EndInvoke(asyncResult);        //Console.WriteLine(result);        Console.ReadKey();    }    public delegate int NewTaskDelegate(int ms);    private static int NewTask(int ms)    {        Console.WriteLine("任务开始");        Thread.Sleep(ms);        Random r = new Random();        int n = r.Next(10000);        Console.WriteLine("任务完成");        return n;    }    private static void MyAsyncCallback(IAsyncResult iar)    {        NewTaskDelegate task = (NewTaskDelegate)iar.AsyncState;        int n = task.EndInvoke(iar);        Console.WriteLine(n);         Console.WriteLine("异步结束。");          }}

}
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