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我已经async void在 ASP.NET Web 窗体页面上成功使用了方法。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 用户控件放入具有async="true"设置的页面时，我不断收到此错误：

此时无法启动异步操作。异步操作只能在异步处理程序或模块内或在页面生命周期中的某些事件期间启动。如果在执行页面时发生此异常，请确保将页面标记为 <%@ Page Async="true" %>。

所以问题是，void async方法可以在 Web 用户控制中使用并嵌入到启用异步的 Web 表单页面中吗？

4

1 回答 1

10

如果它在页面上，您可以让控件调用异步方法。请参见下面的示例：

页面.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 的代码隐藏为空

控制.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();
    }

慢类.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.";
    }
}
于 2013-03-26T21:25:39.820 回答