Xamarin.iOS PostAsync在后台

如何解决Xamarin.iOS PostAsync在后台

我使用Xamarin.Forms / Xamarin.iOS应用向api发送请求。但是，当我将应用程序置于后台而没有api的答案时，PostAsync会引发以下错误：

System.Threading.Tasks.TaskCanceledException: A task was canceled.
  at System.Net.Http.NSUrlSessionHandler.SendAsync (System.Net.Http.HttpRequestMessage request,System.Threading.CancellationToken cancellationToken) [0x001d4] in /Library/Frameworks/Xamarin.iOS.framework/Versions/13.20.2.2/src/Xamarin.iOS/Foundation/NSUrlSessionHandler.cs:527 
  at System.Net.Http.HttpClient.FinishSendAsyncBuffered (System.Threading.Tasks.Task`1[TResult] sendTask,System.Net.Http.HttpRequestMessage request,System.Threading.CancellationTokenSource cts,System.Boolean disposeCts) [0x0017e] in /Library/Frameworks/Xamarin.iOS.framework/Versions/Current/src/Xamarin.iOS/external/corefx/src/System.Net.Http/src/System/Net/Http/HttpClient.cs:506 

我的PostAsync方法是：

public async Task<LoginResponse<LoginDataResponse>> Login(LoginRequest request)
        {
            LoginResponse<LoginDataResponse> responseModel = new LoginResponse<LoginDataResponse>();
            try
            {
                string json = JsonConvert.SerializeObject(request);
                var content = new StringContent(json,Encoding.UTF8,"application/json");

                var jsonBody = await _client.PostAsync(App.ServiceURL.Login_Url,content);
                string jsonstr = await jsonBody.Content.ReadAsStringAsync();

                if (jsonstr == null || jsonstr == "")
                {
                    responseModel.Success = false;
                    responseModel.Status = 0;
                    responseModel.Message = AppResources.UnknownHostException;
                }
                else
                    responseModel = (LoginResponse<LoginDataResponse>)JsonConvert.DeserializeObject(jsonstr,typeof(LoginResponse<LoginDataResponse>));
            }
            catch (Exception ex)
            {
                string text = ex.ToString();
                responseModel.Status = 0;
                AppResources.Culture = CrossMultilingual.Current.CurrentCultureInfo;
                responseModel.Message = AppResources.UnknownHostException;
            }
            return responseModel;
        }

我的系统有一个发送通知的两要素身份验证机制。为了批准通知，我必须将应用程序置于后台。批准通知后，api会返回成功结果。但是，当应用程序进入后台时，我与服务的连接断开。如何在后台继续PostAsync？

解决方法

我找到了解决此问题的方法。我为iOS的HttpClient对象添加了一个配置。此配置为：

if(Device.RuntimePlatform == Device.iOS)
{
    var configuration = NSUrlSessionConfiguration.CreateBackgroundSessionConfiguration ("my.app.identifier");
    _client = new HttpClient (new NSUrlSessionHandler (configuration));
}
else
{
    //android codes
}

我将此客户端对象用于PostAsync。它对我有用。