APM模式，等待異步

Question

我需要關於如何使用APM模式的幫助，我現在正在閱讀一些文章，但我恐怕沒有太多時間。我真正想要的是讓所有的人（從數據庫中的數據），那麼得到的照片，並把它放在一個autocompletebox 代碼：

void listanomesautocomplete(object sender, ServicosLinkedIN.queryCompletedEventArgs e) 
     { 
      if (e.Result[0] != "") 
      { 
       for (int i = 0; i < e.Result.Count(); i = i + 3) 
       { 
        Pessoa pessoa = new Pessoa(); 
        pessoa.Nome = e.Result[i]; 
        pessoa.Id = Convert.ToInt32(e.Result[i + 1]); 
        if (e.Result[i + 2] == "") 
         pessoa.Imagem = new BitmapImage(new Uri("Assets/default_perfil.png", UriKind.Relative)); 
        else 
        { 
         ServicosLinkedIN.ServicosClient buscaimg = new ServicosLinkedIN.ServicosClient(); 
         buscaimg.dlFotoAsync(e.Result[i + 2]); 
         buscaimg.dlFotoCompleted += buscaimg_dlFotoCompleted;//when this completes it saves into a public bitmapimage and then i save it into pessoa.Imagem 
         //basicly, what happends, the listadlfotosasync only happends after this function 
         //what i want is to wait until it completes and have into the class novamsg 
         pessoa.Imagem = img;//saving the photo from dlFotoAsync   

        } 
        listaPessoas.Add(pessoa); 
       } 

       tbA_destinatario.ItemsSource = null; 
       tbA_destinatario.ItemsSource = listaPessoas; 

       BackgroundWorker listapessoas = new BackgroundWorker(); 
       listapessoas.DoWork += listapessoas_DoWork; 
       listapessoas.RunWorkerAsync(); 
       tb_lerdestmsg.Text = ""; 
      } 
      else 
      { 
       tbA_destinatario.ItemsSource = null; 
       tb_lerdestmsg.Text = "Não encontrado"; 
      } 
     } 

Answer 1

有解決這裏的幾件事情：

• listanomesautocomplete事件處理程序應該是async。處理並報告可能拋出的所有異常（通常，這條規則適用於任何事件處理程序，但對於事件處理程序更重要，因爲處理程序內的異步操作會持續到觸發事件的代碼範圍之外） 。

• 先註冊dlFotoCompleted事件處理程序，然後調用dlFotoAsync。不要假設dlFotoAsync將是總是異步執行。

• 想想在另一個listanomesautocomplete被激活而前一個操作仍在等待時的情況。這個井可能會由於用戶的行爲而發生。您可能需要取消並重新啓動掛起的操作（如this），或者只要掛起掛起的掛鉤（如this）就立即排隊新的掛起操作。

回到問題，那就是你需要用爲Task，不APM的EAP pattern。爲此，使用TaskCompletionSource。你的代碼的相關部分可能看起來是這樣的：

async void listanomesautocomplete(object sender, ServicosLinkedIN.queryCompletedEventArgs e) 
{ 
    if (e.Result[0] != "") 
    { 
     for (int i = 0; i < e.Result.Count(); i = i + 3) 
     { 
      Pessoa pessoa = new Pessoa(); 
      pessoa.Nome = e.Result[i]; 
      pessoa.Id = Convert.ToInt32(e.Result[i + 1]); 
      if (e.Result[i + 2] == "") 
       pessoa.Imagem = new BitmapImage(new Uri("Assets/default_perfil.png", UriKind.Relative)); 
      else 
      { 
       // you probably want to create the service proxy 
       // outside the for loop 
       using (ServicosLinkedIN.ServicosClient buscaimg = new ServicosLinkedIN.ServicosClient()) 
       { 
        FotoCompletedEventHandler handler = null; 
        var tcs = new TaskCompletionSource<Image>(); 

        handler = (sHandler, eHandler) => 
        { 
         try 
         { 
          // you can move the code from buscaimg_dlFotoCompleted here, 
          // rather than calling buscaimg_dlFotoCompleted 
          buscaimg_dlFotoCompleted(sHandler, eHandler); 

          tcs.TrySetResult(eHandler.Result); 
         } 
         catch (Exception ex) 
         { 
          tcs.TrySetException(ex); 
         } 
        }; 

        try 
        { 
         buscaimg.dlFotoCompleted += handler; 
         buscaimg.dlFotoAsync(e.Result[i + 2]); 

         // saving the photo from dlFotoAsync 
         pessoa.Imagem = await tcs.Task; 
        } 
        finally 
        { 
         buscaimg.dlFotoCompleted -= handler; 
        } 
       } 
      } 
      listaPessoas.Add(pessoa); 
     } 

     tbA_destinatario.ItemsSource = null; 
     tbA_destinatario.ItemsSource = listaPessoas; 

     BackgroundWorker listapessoas = new BackgroundWorker(); 
     listapessoas.DoWork += listapessoas_DoWork; 
     listapessoas.RunWorkerAsync(); 
     tb_lerdestmsg.Text = ""; 
    } 
    else 
    { 
     tbA_destinatario.ItemsSource = null; 
     tb_lerdestmsg.Text = "Não encontrado"; 
    } 
} 

Answer 2

void listanomesautocomplete(object sender, ServicosLinkedIN.queryCompletedEventArgs e) 
     { 

      if (e.Result[0] != "") 
      { 

       List<Pessoa> listaPessoas = new List<Pessoa>(); 

       for (int i = 0; i < e.Result.Count(); i = i + 3) 
       { 
        Pessoa pessoa = new Pessoa(); 
        pessoa.Nome = e.Result[i]; 
        pessoa.Id = Convert.ToInt32(e.Result[i + 1]); 
        if (e.Result[i + 2] == "") 
         pessoa.Imagem = new BitmapImage(new Uri("Assets/default_perfil.png", UriKind.Relative)); 
        else 
        { 
         ServicosLinkedIN.ServicosClient buscaimg = new ServicosLinkedIN.ServicosClient(); 
         buscaimg.dlFotoAsync(e.Result[i + 2]); 
         //THIS ACTUALLY WORKS!!! 
         //THE THREAD WAITS FOR IT! 
         buscaimg.dlFotoCompleted += (s, a) => 
         { 
          pessoa.Imagem = ConvertToBitmapImage(a.Result); 
         }; 
        } 
        listaPessoas.Add(pessoa); 
       } 

       if (tbA_destinatario.ItemsSource == null) 
       { 

        tbA_destinatario.ItemsSource = listaPessoas; 
       } 
       tb_lerdestmsg.Text = ""; 
      } 
      else 
      { 
       tbA_destinatario.ItemsSource = null; 
       tb_lerdestmsg.Text = "Não encontrado"; 
      } 
     } 

人，我都不生氣，我很驚訝。 Noseratio，你回答給了我一個想法，它實際上工作！ 非常感謝很多人，我不能感謝你足夠;）