异步读取文件

异步读取文件，读取完成之后触发事件，通知主线程。主线程与读取文件的线程互相独立。

using System;
using System.Collections.Generic;
using System.Text;
using System.IO;
using System.Diagnostics;
using System.Threading;

namespace ExToDB.FileTransfer
{
    /// <summary>
    /// 异步读取文件
    /// </summary>
    public class AsyncProcessor
    {
        private Stream inputStream;

        public Stream InputStream
        {
            get { return inputStream; }
            set { inputStream = value; }
        }

        // 每次读取块的大小
        private int bufferSize = 2048;

        public event ReturnEndEvent IsReturnEvent;

        protected void OnIsReturnEvent()
        {
            if (IsReturnEvent != null)
                IsReturnEvent(this, new ReturnEndReadEventargs(true));
        }

        public int BufferSize
        {
            get { return bufferSize; }
            set { bufferSize = value; }
        }

        // 容纳接收数据的缓存
        private byte[] buffer;

        public AsyncProcessor(string fileName)
        {
            buffer = new byte[bufferSize];

            // 打开文件，指定参数为true以提供对异步操作的支持
            inputStream = new FileStream(fileName, FileMode.Open, FileAccess.Read, FileShare.Read, bufferSize, true);
        }

        /// <summary>
        /// 开始读取
        /// </summary>
        public void StartProcess()
        {
            // 开始异步读取文件，填充缓存区
            inputStream.BeginRead(buffer, 0, buffer.Length, OnCompletedRead, null);
        }

        private void OnCompletedRead(IAsyncResult asyncResult)
        {
            // 已经异步读取一个 块 ，接收数据
            int bytesRead = inputStream.EndRead(asyncResult);

            // 如果没有读取任何字节，则流已达文件结尾
            if (bytesRead > 0)
            {
                // 暂停以模拟对数据块的处理
                Debug.WriteLine("   异步线程：已读取一块");
                Thread.Sleep(TimeSpan.FromMilliseconds(20));

                // 开始读取下一块
                inputStream.BeginRead(buffer, 0, buffer.Length, OnCompletedRead, null);
            }
            else
            {
                // 结束操作
                Debug.WriteLine("   异步线程：读取文件结束");
                //读完，触发事件
                OnIsReturnEvent();
                //inputStream.Close();
            }
        }
    }


    public class ReturnEndReadEventargs : EventArgs
    {
        private bool isReturn;

        public ReturnEndReadEventargs(bool isReturn)
        {
            this.isReturn = isReturn;
        }
        public bool IsReturn
        {
            get { return isReturn; }
            set { isReturn = value; }
        }
    }

    public delegate void ReturnEndEvent(object sender, ReturnEndReadEventargs args);
}