如何在Windows Phone 8.1 C＃中停止WebRequest

Question

我刚刚开始开发针对Windows Phone 8.1的应用程序。 在我的应用程序中，我正在调用Web服务并从中获取结果。 但是，当我在Web请求处理过程中单击硬件后退按钮时，该页面将重定向到上一页，但是我无法停止处理Web请求。 得到响应后将显示结果。

我的代码在这里：

  private async void accAcctDet_Click(object sender, RoutedEventArgs e)
    {
                string selected = acct[cmbAccDetail.SelectedIndex];
                string maskselect = cmbAccDetail.SelectedItem.ToString();
                prog.Visibility = Visibility.Visible;    
                acctdetails obj = new acctdetails();
                var result = await obj.GetToken(selected);                   
                if (result.Substring(0, 2) == "Se" || result.Substring(0, 2) == "Ki")
                {
                    prog.Visibility = Visibility.Collapsed;
                    MessageDialog msgbox = new MessageDialog("Service Unavailable. Please try again later", "e-Book!");
                    await msgbox.ShowAsync();
                    ContentRoot.Visibility = Visibility.Visible;
                    myCommandBar.Visibility = Visibility.Visible;
                }
                else
                {
                    prog.Visibility = Visibility.Collapsed;
                    this.Frame.Navigate(typeof(acctdetinfo), result);
                }
    }
    public async Task<string> GetToken(string selected)
    {
        string postData = "selAcct=" + selected;
        var res = await post("myparameter", postData);
        return res;
    }
    private async Task<string> post(string url, string postdata)
    {
        var request = WebRequest.Create(new Uri("myurl.com" + url)) as HttpWebRequest;
        request.Method = "POST";
        request.ContentType = "application/json";
        byte[] data = Encoding.UTF8.GetBytes(postdata);
        //request.ContentLength = data.Length;
        using (var requestStream = await Task<Stream>.Factory.FromAsync(request.BeginGetRequestStream, request.EndGetRequestStream, request))
        {
            await requestStream.WriteAsync(data, 0, data.Length);
        }
        WebResponse responseObject = await Task<WebResponse>.Factory.FromAsync(request.BeginGetResponse, request.EndGetResponse, request);
        var responseStream = responseObject.GetResponseStream(); 
        var sr = new StreamReader(responseStream);
        string received = await sr.ReadToEndAsync();
        return received;
    }

用户单击硬件后退按钮后，我需要停止该请求。

任何帮助将不胜感激

Answer 1

您可以添加一个bool来检查用户是否已离开

//Inside OnNavigatingFrom
...
hasNavigatedAway = true;
...

//Inside post(string url, string postdata)
if(hasNavigatedAway) return;

或者，您也可以使用CancellationToken来执行某些操作，如此处所示 。