I'm using this code to run async function

private async Task SearchMostLessViewsAsync(DateTime dateFrom, DateTime dateTo, int amountOfNumbersSelected, int frequencyOption, int fromDrawNumber, int toDrawNumber)
    {
        Microsoft.AppCenter.Analytics.Analytics.TrackEvent($"{typeof(FragmentDrawsNumbersFrequency).Name}.{nameof(SearchMostLessViewsAsync)}",
            new Dictionary<string, string>()
                {
                    {nameof(dateFrom), dateFrom.ToString()},
                    {nameof(dateTo), dateTo.ToString()},
                    {nameof(amountOfNumbersSelected), amountOfNumbersSelected.ToString()},
                    {nameof(frequencyOption), frequencyOption.ToString()},
                    {nameof(fromDrawNumber), fromDrawNumber.ToString()},
                    {nameof(toDrawNumber), toDrawNumber.ToString()},
                }
            );
        ((MainActivity)Activity).DisplayLoadingMessage(true, GetString(Resource.String.Common_SearchTitle),
            GetString(Resource.String.Common_SearchMessage));

        //ApplicationState.ChangeCancellationTokenSource(new CancellationTokenSource());

        var task = Task.Run(async () =>
        {
            var textResult = await SearchLeast(dateFrom, dateTo, amountOfNumbersSelected, frequencyOption, fromDrawNumber, toDrawNumber).ConfigureAwait(false);

            if (!string.IsNullOrEmpty(textResult))
            {
                UpdateHistoryList(textResult);
                DatabaseFunctions.SaveHistoryList(HistoryList, Settings.DrawsNumbersFrequencyHistoryListViewKey);

                ((MainActivity)Activity).ShowSearchResults(textResult);
            }
        }, ApplicationState.GetCancellationToken()); // Pass same token to Task.Run.

        try
        {
            await task.ConfigureAwait(false);
        }
        catch (TaskCanceledException tce)
        {
            Console.WriteLine($"{nameof(TaskCanceledException)} thrown with message: {tce.Message}");
        }
        catch (System.ObjectDisposedException ode)
        {
            Console.WriteLine($"{nameof(System.ObjectDisposedException)} thrown with message: {ode.Message}");
        }
        catch (System.OperationCanceledException e)
        {
            Console.WriteLine($"{nameof(System.OperationCanceledException)} thrown with message: {e.Message}");
        }
        catch (NullReferenceException nre)
        {
            Console.WriteLine($"{nameof(NullReferenceException)} thrown with message: {nre.Message}");
        }
        finally
        {
            ApplicationState.DisposeCancellationTokenSource();
            ((MainActivity)Activity).DisplayLoadingMessage(false);
        }

        ((MainActivity)Activity).DisplayLoadingMessage(false);
    }

But sometimes i get this exception

FragmentDrawsNumbersFrequency.SearchMostLessViewsAsync (System.DateTime dateFrom, System.DateTime dateTo, System.Int32 amountOfNumbersSelected, System.Int32 frequencyOption, System.Int32 fromDrawNumber, System.Int32 toDrawNumber)
FragmentDrawsNumbersFrequency.ShowMostLessViews ()
FragmentDrawsNumbersFrequency.<OnCreateView>b__50_8 (System.Object sender, System.EventArgs e)
AsyncMethodBuilderCore <>c.<ThrowAsync>b__7_0 (System.Object state)
SyncContext <>c__DisplayClass2_0.<Post>b__0 ()
Thread RunnableImplementor.Run ()
IRunnableInvoker.n_Run (System.IntPtr jnienv, System.IntPtr native__this)
(wrapper dynamic-method) Android.Runtime.DynamicMethodNameCounter.61(intptr,intptr)

I'm not sure why. Shouldn't the try catch wrap catch nullreference exceptions?

CodePudding user response：

Currently you would catch NullReferenceException only if task is null, which obviously isn't the case.

You probably want to do try/catch inside the task.