C#多线程之异步编程

   c#中异步编程,主要有两种方法: 1、委托的异步调用; 2、Task的await,async (c# 4.5)

 我们来看例子:

1         /// <summary>
2         /// 异步保存网页,url:网页地址,path:要保存的位置
3         /// </summary>
4         private void SavePageAsync(string url, string path)
5         {
6             Func<string, string, bool> fun = SavePageSingleFile;
7             IAsyncResult result = fun.BeginInvoke(url, path, new AsyncCallback(SavePageCompleted), null);
8         }

Func,是系统定义好的委托类型,当然也可以自定义委托了,委托的本质是一个类,它有一个BeginInvoke 异步调用方法。SavePageSingleFile方法是委托要执行的方法:

 1         private bool SavePageSingleFile(string url, string path)
 2         {
 3             bool result = false;
 4             try
 5             {
 6                 CDO.Message message = new CDO.MessageClass();
 7                 ADODB.Stream stream = null;
 8                 message.MimeFormatted = true;
 9                 message.CreateMHTMLBody(url, CDO.CdoMHTMLFlags.cdoSuppressNone, "", "");
10                 stream = message.GetStream();
11                 stream.SaveToFile(path, ADODB.SaveOptionsEnum.adSaveCreateOverWrite);
12                 message = null;
13                 stream.Close();
14 
15                 result = true;
16             }
17             catch (Exception ex)
18             {
19                 Logger.Debug("保存文件出错:" + ex.Message);
20             }
21             return result;
22         }
  
委托任务完成后的回调方法 SavePageCompleted:
 1       private void SavePageCompleted(IAsyncResult result)
 2        {
 3             try
 4             {
 5                 var handler = (Func<string, string, bool>)((AsyncResult)result).AsyncDelegate;
 6                 var r = handler.EndInvoke(result);
 7 
 8                 this.Dispatcher.BeginInvoke(DispatcherPriority.Normal,
 9                                    (ThreadStart)delegate()
10                                    {
11                                        this.Opacity = 1;
12 
13                                        if (CloseWaittingWindow != null)
14                                        {
15                                            CloseWaittingWindow();
16                                        }
17                                        this.Cursor = System.Windows.Input.Cursors.Hand;
18 
19                                        MessageTip tip = new MessageTip();
20                                        if (r)
21                                        {
22                                            tip.Show("保存网页", "文件保存成功");
23                                        }
24                                        else
25                                        {
26                                            tip.Show("保存网页", "文件保存失败");
27                                        }
28                                    }
29                           );
30             }
31             catch (Exception ex)
32             {
33                 Logger.Debug("保存页面文件出错:" + ex.Message);
34                 this.Dispatcher.BeginInvoke(DispatcherPriority.Normal,
35                                  (ThreadStart)delegate()
36                                  {
37                                      new MessageTip().Show("保存网页", "文件保存出错");
38                                      this.Opacity = 1;
39 
40                                      if (CloseWaittingWindow != null)
41                                      {
42                                          CloseWaittingWindow();
43                                      }
44                                      this.Cursor = System.Windows.Input.Cursors.Hand;
45                                  }
46                         );
47             }
48         }

最后看下 SavePageAsync 方法的调用:

 1         /// <summary>
 2         /// 保存当前页面
 3         /// </summary>
 4         /// <param name="sender"></param>
 5         /// <param name="e"></param>
 6         private void btnSavePage_Click(object sender, RoutedEventArgs e)
 7         {
 8             if (this.DBVisitViewModel.CanSavePageExcute)
 9             {
10                 string url = this.WebPageBrower.Url.AbsoluteUri;
11                 if (!Tool.CheckUrl(url))
12                 {
13                     new MessageTip().Show("保存页面", "当前页面无法保存");
14                     return;
15                 }
16 
17                 SaveFileDialog sfd = new SaveFileDialog();
18 
19                 sfd.InitialDirectory = @"D:\";
20                 sfd.Filter = "mht file|*.mht";
21 
22                 if (sfd.ShowDialog() == DialogResult.OK)
23                 {
24                     if (OpenWaittingWindow != null)
25                     {
26                         this.Cursor = System.Windows.Input.Cursors.Wait;
27                         SavePageAsync(url, sfd.FileName);
28 
29                         this.Opacity = 0.8;
30                         OpenWaittingWindow("正在保存网页,请稍等...");
31                     }
32                 }
33             }
34         }

 

在framework 4.0的时候,委托异步调用显得很方便,到了4.5的时候,我们可以用Task实现异步调用。改下上面的例子:

 1        private async void SavePageAsync(string url, string path)
 2         {
 3             var r = await SavePageSingleFile(url, path);
 4 
 5             try
 6             {
 7                 this.Dispatcher.BeginInvoke(DispatcherPriority.Normal,
 8                                    (ThreadStart)delegate()
 9                                    {
10                                        this.Opacity = 1;
11 
12                                        if (CloseWaittingWindow != null)
13                                        {
14                                            CloseWaittingWindow();
15                                        }
16                                        this.Cursor = System.Windows.Input.Cursors.Hand;
17 
18                                        MessageTip tip = new MessageTip();
19                                        if (r)
20                                        {
21                                            tip.Show("保存网页", "文件保存成功");
22                                        }
23                                        else
24                                        {
25                                            tip.Show("保存网页", "文件保存失败");
26                                        }
27                                    }
28                           );
29             }
30             catch (Exception ex)
31             {
32                 Logger.Debug("保存页面文件出错:" + ex.Message);
33                 this.Dispatcher.BeginInvoke(DispatcherPriority.Normal,
34                                  (ThreadStart)delegate()
35                                  {
36                                      new MessageTip().Show("保存网页", "文件保存出错");
37                                      this.Opacity = 1;
38 
39                                      if (CloseWaittingWindow != null)
40                                      {
41                                          CloseWaittingWindow();
42                                      }
43                                      this.Cursor = System.Windows.Input.Cursors.Hand;
44                                  }
45                         );
46             }
47 
48 
49 
50         }
51         static async Task<bool> SavePageSingleFile(string url, string path)
52         {
53             return await Task.Run(() =>
54             {
55                 bool result = false;
56                 try
57                 {
58                     CDO.Message message = new CDO.MessageClass();
59                     ADODB.Stream stream = null;
60                     message.MimeFormatted = true;
61                     message.CreateMHTMLBody(url, CDO.CdoMHTMLFlags.cdoSuppressNone, "", "");
62                     stream = message.GetStream();
63                     stream.SaveToFile(path, ADODB.SaveOptionsEnum.adSaveCreateOverWrite);
64                     message = null;
65                     stream.Close();
66 
67                     result = true;
68                 }
69                 catch (Exception ex)
70                 {
71                     Logger.Debug("保存文件出错:" + ex.Message);
72                 }
73                 return result;
74             });
75         }

第5行后的try,catch语句块,就是保存网页后的回调,它的执行是在子线程中,因此,在wpf 中要用 Dispatcher(回调中牵扯到对页面的操作)。为了简化这一例子,我这儿给出一个简单的可以执行的例子:

 1   static void Main(string[] args)
 2         {
 3             Add(2,3);
 4             Console.WriteLine("主线程:" + Thread.CurrentThread.ManagedThreadId);
 5             Console.WriteLine("main Thread go on sth"); 
 6             Console.Read();
 7         }
 8 
 9         private async static void Add(int x, int y)
10         {
11             Console.WriteLine("主线程:" + Thread.CurrentThread.ManagedThreadId);
12             var t = await TestAsync(x,y);
13             Console.WriteLine("正在等待完成任务,当前线程:"+Thread.CurrentThread.ManagedThreadId);
14 
15             Console.WriteLine("运行结果:" + t);                      
16         }
17         static async Task<int> TestAsync(int x, int y)
18         {
19             return await Task.Run(() =>
20             {
21                 Thread.Sleep(1000);
22                 Console.WriteLine("子线程:" + Thread.CurrentThread.ManagedThreadId);
23                 return x + y;                         
24             });
25         }

运行结果:

异步编程主要是为了解决耗时的任务占用主线程的问题,比如ajax的异步调用,不会导致页面卡死。好了,今天就谈到这里,该吃中午饭了。

 

posted @ 2017-11-10 11:45  micDavid  阅读(312)  评论(0编辑  收藏  举报