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。
时间： 2024-10-08 01:30:30