如何在Windows Phone 8.1 C＃中停止WebRequest

Question

我剛剛開始開發針對Windows Phone 8.1的應用程序。 在我的應用程序中，我正在調用Web服務並從中獲取結果。 但是，當我在Web請求處理過程中單擊硬件后退按鈕時，該頁面將重定向到上一頁，但是我無法停止處理Web請求。 得到響應后將顯示結果。

我的代碼在這里：

  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;
    }

用戶單擊硬件后退按鈕后，我需要停止該請求。

任何幫助將不勝感激

Answer 1

您可以添加一個bool來檢查用戶是否已離開

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

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

或者，您也可以使用CancellationToken來執行某些操作，如此處所示 。