学步园

namespace System
{
    // Summary:
    //     Represents the status of an asynchronous operation.
    [ComVisible(true)]
    public interface IAsyncResult
    {
        // Summary:
        //     Gets a user-defined object that qualifies or contains information about an
        //     asynchronous operation.
        //
        // Returns:
        //     A user-defined object that qualifies or contains information about an asynchronous
        //     operation.
        object AsyncState { get; }
        //
        // Summary:
        //     Gets a System.Threading.WaitHandle that is used to wait for an asynchronous
        //     operation to complete.
        //
        // Returns:
        //     A System.Threading.WaitHandle that is used to wait for an asynchronous operation
        //     to complete.
        WaitHandle AsyncWaitHandle { get; }
        //
        // Summary:
        //     Gets a value that indicates whether the asynchronous operation completed
        //     synchronously.
        //
        // Returns:
        //     true if the asynchronous operation completed synchronously; otherwise, false.
        bool CompletedSynchronously { get; }
        //
        // Summary:
        //     Gets a value that indicates whether the asynchronous operation has completed.
        //
        // Returns:
        //     true if the operation is complete; otherwise, false.
        bool IsCompleted { get; }
    }
}

        static void Main(string[] args)
        {

            //利用了已经实现了IAsyncResult异步模式的.NET自带的组件WebRequest
            String UserInputUrl = "";
            String FileName = "";
            Console.WriteLine("输入URL启动一个异步下载Web文件任务，输入quit退出.");
            do
            {
                Console.Write("\n输入Web文件的URL：");
                UserInputUrl = Console.ReadLine();

                if (String.IsNullOrWhiteSpace(UserInputUrl))
                {
                    Console.WriteLine("不能输入一个空的URL字符串");
                    continue;
                }
                if (UserInputUrl.ToLower() == "quit")
                {
                    break;
                }
                Console.Write("请输入要保存的文件名:");
                FileName = Console.ReadLine();
                if (String.IsNullOrWhiteSpace(FileName))
                {
                    Console.WriteLine("不能输入一个空的URL字符串");
                    continue;
                }
                try
                {
                    Uri webFileUri = new Uri(UserInputUrl);
                    WebRequest webRequest = WebRequest.Create(webFileUri);
                    DownLoadTask task = new DownLoadTask { SaveToFileName = FileName, WebRequestObject = webRequest };
                    Console.WriteLine("已在后台自动下载{0}", FileName);
                    webRequest.BeginGetResponse(DownloadFinished, task);
                }
                catch (Exception ex)
                {

                    Console.WriteLine(ex.Message);
                }

            } while (true);

            Console.ReadKey();

        }


        static void DownloadFinished(IAsyncResult ar)
        {
            try
            {
                DownLoadTask task = ar.AsyncState as DownLoadTask;
                WebResponse response = task.WebRequestObject.EndGetResponse(ar);
                String FileContent = "";
                using (StreamReader reader = new StreamReader(response.GetResponseStream(), Encoding.GetEncoding("gb2312")))
                {
                    FileContent = reader.ReadToEnd();
                }

                using (StreamWriter writer = new StreamWriter(new FileStream(task.SaveToFileName, FileMode.Create), Encoding.GetEncoding("gb2312")))
                {
                    writer.Write(FileContent);
                }

                MessageBox.Show(String.Format("{0}下载完成！", task.SaveToFileName));

            }
            catch (Exception ex)
            {

                throw new Exception(ex.Message);

            }
        }

//异步测试 创建委托对象后，调用BeginInvoke方法，循环检查是否完成，没完成则处理win消息。完成后调用EndInvoke获取结果并处理。

        private delegate bool SendCommandHandler(string command, ref string response);

        private bool SendCommand(string command, ref string response)
        {
            Thread.Sleep(1000);
            response = command;
            if(command.Length != 0)
                throw new Exception("Error");
            return true;
        }

        private void button1_Click_1(object sender, EventArgs e)
        {
            SendCommandHandler handler = SendCommand;
            string response = "";
            IAsyncResult result = handler.BeginInvoke("hello world", ref response, null, null);
            while (!result.IsCompleted)
                Application.DoEvents();
            try
            {
                handler.EndInvoke(ref response, result);
                MessageBox.Show(response);
            }
            catch (System.Exception ex)
            {
                
            }
            
        }