WebForms上的異步行爲gridview

Question

將傳統應用程序移植到異步\ await模式時，我們遇到了一些我們無法跟蹤的奇怪行爲。我們將頁面async指令設置爲true，並向RowDataBound添加事件處理程序。如果EventHandler中的代碼包含等待的呼叫，則在繼續處理下一行之前，不會等待它。

這裏是一個攝製，使其更易於理解：

public partial class WorkingCorrectlyWebForm: System.Web.UI.Page 
{ 
    private int _index; 
    protected void Page_Load(object sender, EventArgs e) 
    { 
     var grid = new GridView(); 
     grid.RowDataBound += GridOnRowDataBound; 
     grid.DataSource = new[] 
     { 
      new {Name = "Person1", Age = 23}, 
      new {Name = "Person2", Age = 33}, 
      new {Name = "Person3", Age = 15} 
     }; 

     grid.DataBind(); 
    } 

    private async void GridOnRowDataBound(object sender, GridViewRowEventArgs gridViewRowEventArgs) 
    { 
     if (gridViewRowEventArgs.Row.RowType != DataControlRowType.DataRow) 
      return; 

     var localIndex = ++_index; 

     HttpContext.Current.Response.Write($"starting #{localIndex} <br />"); 

     await Task.Delay(1000); //HERE IS THE PROBLEMATIC LINE 

     //removing the remark from the following line will make code behave "synchronously" as expected. 
     // Task.Delay(1000).Wait(); 

     HttpContext.Current.Response.Write($"exiting #{localIndex} <br />"); 
    } 
} 

此代碼將產生輸出類同這個（而不是命令「開始\退出」每一個項目）：

出發＃1

起始＃2

起始＃3

離開＃3

離開＃1

離開＃2

這是爲什麼happeninig？爲什麼我沒有看到有序的「開始」和「退出」消息。

Answer 1

如果你想連續的行爲，這應該工作：

private void GridOnRowDataBound(object sender, GridViewRowEventArgs gridViewRowEventArgs) 
    { 
     if (gridViewRowEventArgs.Row.RowType != DataControlRowType.DataRow) 
      return; 

     var localIndex = ++_index; 

     HttpContext.Current.Response.Write($"starting #{localIndex} <br />"); 

     Thread.Sleep(1000); 
     // or    Task.Delay(1000).Wait(); 


     HttpContext.Current.Response.Write($"exiting #{localIndex} <br />"); 
    } 

或嘗試：

private void GridOnRowDataBound(object sender, GridViewRowEventArgs gridViewRowEventArgs) 
    { 
     RegisterAsyncTask(new PageAsyncTask(() => Bob(gridViewRowEventArgs))); 
     HttpContext.Current.Response.Write($"b"); 

    } 

    private async Task Bob(GridViewRowEventArgs gridViewRowEventArgs) 
    { 
     if (gridViewRowEventArgs.Row.RowType != DataControlRowType.DataRow) 
      return; 

     var localIndex = ++_index; 

     HttpContext.Current.Response.Write($"starting #{localIndex} <br />"); 

     await Task.Delay(1000); 

     HttpContext.Current.Response.Write($"exiting #{localIndex} <br />"); 
    }