C# WebForms gridview上的异步行为

在将遗留应用程序移植到async\Wait模式时，我们遇到了一些无法跟踪的奇怪行为。我们将page async指令设置为true，并将事件处理程序添加到RowDataBound。如果EventHandler中的代码包含等待调用，则在继续处理下一行之前不会等待调用

下面是一个更容易理解的程序：

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 />");
    }
}

此代码将生成与此类似的输出，而不是按顺序开始\退出每个项目：

开始1

开始2

开始3

退出3

退出1

退出2

---

为什么会这样？为什么我看不到有序的启动和退出消息。

如果需要串行行为，这应该可以：

    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 />");
    }

或者尝试：

    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 />");
    }

---

等待任务.Delay1000只是为了重新编程。这意味着在这种情况下，任何等待的电话都不会被等待。请看“我的问题”。我在那里写道，这是可行的，但我的问题是，为什么Wait在这个场景中不能像我预期的那样工作。我怀疑这是因为您已将该方法标记为async。您希望该方法是异步的，有什么特别的原因吗？是的，因为它需要在等待的方法上等待。您不能只使用等待的方法。等等？