private void Form1_Load(object sender, EventArgs e)
        {
            System.Diagnostics.Stopwatch sw = new System.Diagnostics.Stopwatch();
            const int SIZE = 10;        //方便测试这里设置小一点
            var input = "AWfs测试_fs2测试AS测试34再测试一下;&)$@Lrwer{DWUEND.";
            var buffer = new byte[SIZE];
            var chars = Encoding.UTF8.GetChars(buffer);     //其实是Size的一半，C#中一个字符占两字节
            //AsyncCallback callBack = args =>
            //{
            //    //弄了个listBox反馈结果
             //    if (this.listBox1.InvokeRequired)
            //        this.listBox1.Invoke(new Action(() => this.listBox1.Items.Add(string.Format("\r\nHad written file: {0}.txt", (int)args.AsyncState))));
            //};
            sw.Start();
            using (var sr = new System.IO.StringReader(input))
            {
                int offset = 0, times = 0;
                IAsyncResult asyResult = null;
                while (times < 10 && sr.Peek() > -1)
                {
                    //读到的字符数量，上面忽略了它，在最后一个文件会有bug
                    offset = sr.Read(chars, 0, chars.Length);
                    buffer = Encoding.UTF8.GetBytes(chars, 0, offset);
                    using (var fs = new FileStream(Application.StartupPath + "\\" + ++times + ".txt", FileMode.Create))
                    {
                        //异步写数据，无回调
                        //asyResult = fs.BeginWrite(buffer, 0, offset, callBack, times);
                        asyResult = fs.BeginWrite(buffer, 0, buffer.Length, null, null);
                        fs.EndWrite(asyResult);
                        fs.Flush();
                        fs.Close();
                    }
                 }
            }
            sw.Stop();
            this.label1.Text = sw.ElapsedTicks.ToString(); 
            //上面那个用了回调是2001392 左右，去掉后38563，提升很多     
        }