Question

假设我有一个包含多个标签的GroupBox。在这些标签中，显示各种与IP相关的信息。一个信息是机器的外部IP地址。

string externalIP = "";

try
{
    WebRequest request = WebRequest.Create("http://checkip.dyndns.org/");
    request.Timeout = 3000;
    System.Threading.Tasks.Task<System.Net.WebResponse> response =  request.GetResponseAsync();

    using (StreamReader stream = new StreamReader(response.Result.GetResponseStream()))
    {
        if (response.Result.ContentLength != -1)
        {
             externalIP = stream.ReadToEnd();
        }
    }               
}
catch (Exception e)
{
    externalIP = "Error.";
}

if (externalIP == "")
{
    return "No service.";
}
else
{
    return externalIP = (new Regex(@"\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}")).Matches(externalIP)[0].ToString();
}

从以下代码调用此方法：

private void updateNetworkIP()
{ 
    string ip4e = "External IPv4: " + getExternalIPv4();
    lblIP4external.Text = ip4e;

    //Get some more info here.
}

如果在getExternalIPv4（）之后执行代码，即使它尚未完成，我该怎么办？它像我上面那样设置TimeOut时有效，但有时候请求只需要一点时间但仍能成功完成。所以我希望仍然能够显示外部IP，但继续执行其他方法来刷新GroupBox。

Answer 1

BackgroundWorker将提供您所追求的目标。示例代码：

BackgroundWorker bg = new BackgroundWorker();
bg.DoWork += new DoWorkEventHandler(getExternalIPv4Back);
bg.RunWorkerCompleted += new RunWorkerCompletedEventHandler(writeLabel);
bg.RunWorkerAsync();
//The code below this point will be executed while the BackgroundWorker does its work

您必须将getExternalIPv4Back定义为DoWork Event Method并在其中包含要并行执行的代码;还writeLabel作为RunWorkerCompleted Event（需要编辑标签而不会引发与多线程相关的错误）。那就是：

private void getExternalIPv4Back(object sender, DoWorkEventArgs e)
{
    IP = "External IPv4: " + getExternalIPv4(); //IP -> Globally defined variable
}

private void writeLabel(object sender, RunWorkerCompletedEventArgs e)
{
   lblIP4external.Text = IP;
}

如何在不等待其他操作完成的情况下更新视图

1 个答案: