Question

我在ASP.NET Web窗体页面上成功使用了async void方法。但是，当我尝试在Web用户控件中使用相同的方法，然后将此Web用户控件放到设置为async="true"的页面时，我不断收到此错误：

此时无法启动异步操作。异步操作可能只能在异步中启动处理程序或模块或在页面生命周期中的某些事件期间。如果执行页面时发生此异常，确保页面标记为＆lt;％@ Page Async =“true”％＆gt;。

所以问题是，可以在Web用户控件中使用void async方法并将其嵌入到启用异步的Web表单页面中吗？

Answer 1

如果它在页面上，您可以拥有控制调用异步方法。请参阅以下示例：

<强> Page.aspx

<%@ Page Language="C#" AutoEventWireup="true" CodeBehind="Page.aspx.cs" Inherits="AsyncDEmo.Page" Async="true" %>

<%@ Register Src="~/Control.ascx" TagPrefix="uc1" TagName="Control" %>

<!DOCTYPE html>

<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
    <title></title>
</head>
<body>
    <form id="form1" runat="server">
        <uc1:Control runat="server" id="Control" />
    </form>
</body>
</html>

Page.aspx的代码隐藏是空的

<强> Control.ascx

<%@ Control Language="C#" AutoEventWireup="true" CodeBehind="Control.ascx.cs" Inherits="AsyncDEmo.Control" %>

<span id="TaskMessage" runat="server">
      </span>

控制代码隐藏

protected void Page_Load(object sender, EventArgs e)
    {
        // Define the asynchronuous task.
        Samples.AspNet.CS.Controls.SlowTask slowTask1 =
          new Samples.AspNet.CS.Controls.SlowTask();
        Samples.AspNet.CS.Controls.SlowTask slowTask2 =
        new Samples.AspNet.CS.Controls.SlowTask();
        Samples.AspNet.CS.Controls.SlowTask slowTask3 =
        new Samples.AspNet.CS.Controls.SlowTask();

        PageAsyncTask asyncTask1 = new PageAsyncTask(slowTask1.OnBegin, slowTask1.OnEnd, slowTask1.OnTimeout, "Async1", true);
        PageAsyncTask asyncTask2 = new PageAsyncTask(slowTask2.OnBegin, slowTask2.OnEnd, slowTask2.OnTimeout, "Async2", true);
        PageAsyncTask asyncTask3 = new PageAsyncTask(slowTask3.OnBegin, slowTask3.OnEnd, slowTask3.OnTimeout, "Async3", true);

        // Register the asynchronous task.
        Page.RegisterAsyncTask(asyncTask1);
        Page.RegisterAsyncTask(asyncTask2);
        Page.RegisterAsyncTask(asyncTask3);

        // Execute the register asynchronous task.
        Page.ExecuteRegisteredAsyncTasks();

        TaskMessage.InnerHtml = slowTask1.GetAsyncTaskProgress() + "<br />" + slowTask2.GetAsyncTaskProgress() + "<br />" + slowTask3.GetAsyncTaskProgress();
    }

<强> SlowClass.cs

public class SlowTask
{
    private String _taskprogress;
    private AsyncTaskDelegate _dlgt;

    // Create delegate. 
    protected delegate void AsyncTaskDelegate();

    public String GetAsyncTaskProgress()
    {
        return _taskprogress;
    }
    public void ExecuteAsyncTask()
    {
        // Introduce an artificial delay to simulate a delayed  
        // asynchronous task.
        Thread.Sleep(TimeSpan.FromSeconds(5.0));
    }

    // Define the method that will get called to 
    // start the asynchronous task. 
    public IAsyncResult OnBegin(object sender, EventArgs e,
        AsyncCallback cb, object extraData)
    {
        _taskprogress = "AsyncTask started at: " + DateTime.Now + ". ";

        _dlgt = new AsyncTaskDelegate(ExecuteAsyncTask);
        IAsyncResult result = _dlgt.BeginInvoke(cb, extraData);

        return result;
    }

    // Define the method that will get called when 
    // the asynchronous task is ended. 
    public void OnEnd(IAsyncResult ar)
    {
        _taskprogress += "AsyncTask completed at: " + DateTime.Now;
        _dlgt.EndInvoke(ar);
    }

    // Define the method that will get called if the task 
    // is not completed within the asynchronous timeout interval. 
    public void OnTimeout(IAsyncResult ar)
    {
        _taskprogress += "AsyncTask failed to complete " +
            "because it exceeded the AsyncTimeout parameter.";
    }
}

可以在ASP.NET用户控件中使用void异步方法吗？

1 个答案: