Web客户端的DownloadStringCompleted事件处理程序不开火(Webclient&

我创造出几个设备和网站（上，下等）的状态Silverlight的仪表板。我试图使用WebClient类连接到一个网站，看看它是否到了。但DownloadStringCompleted事件处理程序永远不会被解雇。这是一个非常类似的问题到这个职位。

public void LoadPortalStatus(Action<IEnumerable<ChartModel>> success, Action<Exception> fail)
{
    List<NetworkPortalStatusModel> pingedItems = new List<NetworkPortalStatusModel>();

    // Add the status for the portal
    BitmapImage bi = IsPortalActive() 
            ? (new BitmapImage(new Uri("led_green_black-100x100.png", UriKind.Relative))) 
            : (new BitmapImage(new Uri("led_red_black-100x100.png", UriKind.Relative)));

    NetworkPortalStatusModel nsm = new NetworkPortalStatusModel
    {
        Unit = "Portal",
        StatusIndicator = new Image { Width = 100, Height = 100, Source = bi }
    };

    pingedItems.Add(nsm);

    // Send back to the UI thread
    System.Windows.Deployment.Current.Dispatcher.BeginInvoke(_delagateSuccess, new object[] { pingedItems });
}

private bool IsPortalActive()
{
    bool IsActive = false;

    WebClient wc = new WebClient();
    wc.DownloadStringCompleted += (s, e) =>
        {
            if (e.Cancelled) 
            {
                _delagateFail(new Exception("WebClient page download cancelled"));
            }
            else if (e.Error != null)
            {
                _delagateFail(e.Error);
            }
            else
            {
                _portalHtmlResponse = e.Result;
                if (_portalHtmlResponse.Contains("Somerville, Ma"))
                {
                    IsActive = true;
                }
            }
        };
    wc.DownloadStringAsync(new Uri("https://portal.nbic.com/monitor.aspx"));

    return IsActive;
}

有谁看到这里的问题？

你想哄异步方法调用转换为同步方法 - 它是行不通的，因为该方法将Web客户端的完成回调之前返回有机会执行。

使用Silverlight，你应该接受异步。要做到这一点的方法之一是通过在运行一次字符串已经被下载你想要执行的代码的延续委托。