Exception thrown: 'System.TypeLoadException' in Unknown Module in UWP Background Task

问题

This code gives me the exception

Exception thrown: 'System.TypeLoadException' in Unknown Module

public sealed class SampleBackgroundTask2 : IBackgroundTask
{

        EasClientDeviceInformation currentDeviceInfo;

        BackgroundTaskCancellationReason _cancelReason = BackgroundTaskCancellationReason.Abort;

        BackgroundTaskDeferral _deferral = null;

        IBackgroundTaskInstance _taskInstance = null;

        ThreadPoolTimer _periodicTimer = null;

        //
        // The Run method is the entry point of a background task.
        //
        public void Run(IBackgroundTaskInstance taskInstance)
        {
            currentDeviceInfo = new EasClientDeviceInformation();

            var cost = BackgroundWorkCost.CurrentBackgroundWorkCost;
            var settings = ApplicationData.Current.LocalSettings;
            settings.Values["BackgroundWorkCost2"] = cost.ToString();

            taskInstance.Canceled += new BackgroundTaskCanceledEventHandler(OnCanceled);

            _deferral = taskInstance.GetDeferral();
            _taskInstance = taskInstance;

            _periodicTimer = ThreadPoolTimer.CreateTimer(new TimerElapsedHandler(PeriodicTimerCallbackAsync), TimeSpan.FromSeconds(1));
        }

        private async void PeriodicTimerCallbackAsync(ThreadPoolTimer timer)
        {
            try
            {
                var httpClient = new HttpClient(new HttpClientHandler()); 

                string urlPath = (string)ApplicationData.Current.LocalSettings.Values["ServerIPAddress"] + "/Api/Version1/IsUpdatePersonal";

                HttpResponseMessage response = await httpClient.PostAsync(urlPath,
                    new StringContent(JsonConvert.SerializeObject(currentDeviceInfo.Id.ToString()), Encoding.UTF8, "application/json")); // new FormUrlEncodedContent(values)

                response.EnsureSuccessStatusCode();

                if (response.IsSuccessStatusCode)
                {
                    string jsonText = await response.Content.ReadAsStringAsync();
                    var customObj = JsonConvert.DeserializeObject<bool>(jsonText, new JsonSerializerSettings() { TypeNameHandling = TypeNameHandling.All });

                    if (customObj) // Если TRUE  то да надо сообщить пользователю о необходимости обновления
                    {
                        ShowToastNotification("Ttitle", "Message");
                    }
                }
            }
            catch (HttpRequestException ex)
            {
            }
            catch (Exception ex)
            {
            }
            finally
            {
                _periodicTimer.Cancel();
                _deferral.Complete();
            }
        }

private void OnCanceled(IBackgroundTaskInstance sender, BackgroundTaskCancellationReason reason)
        {
            _cancelReason = reason;
        }
}

If I comment async/await and HttpClient places then there is no exception.

So what's wrong with my code? Or Is it done well to use UWP Background Task to make async GET/POST?

I have tried some classic solution like

public async void Run(IBackgroundTaskInstance taskInstance)
{
 BackgroundTaskDeferral _deferral = taskInstance.GetDeferral();
 //
 // Start one (or more) async
 // Use the await keyword
 //
 // await SomeMethodAsync();


        var uri = new System.Uri("http://www.bing.com");
        using (var httpClient = new Windows.Web.Http.HttpClient())
        {
            // Always catch network exceptions for async methods
            try
            {
                string result = await httpClient.GetStringAsync(uri);
            }
            catch (Exception ex)
            {
                // Details in ex.Message and ex.HResult.
            }
        }


 _deferral.Complete();
}

but once I put HttpClient inside of SomeMethodAsync() it does not work with the error above.

This solution does not help HttpClient.GetAsync fails in background task with lock screen access and both TimeTrigger or MaintenanceTrigger

Thanks!

回答1:

I simplified the solution a bit and removed the ThreadPoolTimer since I was not sure why it was being used from the code. Please mention if it is required for the solution.

If the ThreadPoolTimer is optional then you can try the following code :

public sealed class SampleBackgroundTask2 : IBackgroundTask
    {

        EasClientDeviceInformation currentDeviceInfo;

        BackgroundTaskCancellationReason _cancelReason = BackgroundTaskCancellationReason.Abort;

        BackgroundTaskDeferral _deferral = null;

        //
        // The Run method is the entry point of a background task.
        //
        public async void Run(IBackgroundTaskInstance taskInstance)
        {
            currentDeviceInfo = new EasClientDeviceInformation();

            var cost = BackgroundWorkCost.CurrentBackgroundWorkCost;
            var settings = ApplicationData.Current.LocalSettings;
            settings.Values["BackgroundWorkCost2"] = cost.ToString();

            taskInstance.Canceled += new BackgroundTaskCanceledEventHandler(OnCanceled);

            _deferral = taskInstance.GetDeferral();
            await asynchronousAPICall();
            _deferral.Complete(); //calling this only when the API call is complete and the toast notification is shown
        }
        private async Task asynchronousAPICall()
        {
            try
            {
                var httpClient = new HttpClient(new HttpClientHandler());

                string urlPath = (string)ApplicationData.Current.LocalSettings.Values["ServerIPAddress"] + "/Api/Version1/IsUpdatePersonal";

                HttpResponseMessage response = await httpClient.PostAsync(urlPath,
                    new StringContent(JsonConvert.SerializeObject(currentDeviceInfo.Id.ToString()), Encoding.UTF8, "application/json")); // new FormUrlEncodedContent(values)

                response.EnsureSuccessStatusCode();

                if (response.IsSuccessStatusCode)
                {
                    string jsonText = await response.Content.ReadAsStringAsync();
                    var customObj = JsonConvert.DeserializeObject<bool>(jsonText, new JsonSerializerSettings() { TypeNameHandling = TypeNameHandling.All });

                    if (customObj) // Если TRUE  то да надо сообщить пользователю о необходимости обновления
                    {
                        ShowToastNotification("Ttitle", "Message");
                    }
                }
            }
            catch (HttpRequestException ex)
            {
            }
            catch (Exception ex)
            {
            }
            finally
            {
                _deferral.Complete();
            }
        }

        private void OnCanceled(IBackgroundTaskInstance sender, BackgroundTaskCancellationReason reason)
        {
            _cancelReason = reason;
        }
    }

Please let me know if this works for you.

来源：https://stackoverflow.com/questions/54759390/exception-thrown-system-typeloadexception-in-unknown-module-in-uwp-background