c# - Task> 不包含 where 的定义

Question

我正在尝试按保存在其中的日期过滤可观察集合。用户将使用日历 View 选择日期。

public async Task RefreshItems(bool showActivityIndicator, bool syncItems)
        {
            using (var scope = new ActivityIndicatorScope(syncIndicator, showActivityIndicator))
            {

                var items = manager.GetAppointmentItemsAsync();


                CalendarVM vm = new CalendarVM();
                calendar.SetBinding(Calendar.DateCommandProperty, nameof(vm.DateChosen));
                calendar.SetBinding(Calendar.SelectedDateProperty, nameof(vm.DateSelected));
                calendar.BindingContext = vm;

                var filtered = items.Where(appointmentItem => appointmentItem.Date == SelectedDate);
            }
        }

以下是 AppointmentPage 类中的代码，其中包含用户选择的日期和数据。

  public async Task<ObservableCollection<AppointmentItem>> GetAppointmentItemsAsync(bool syncItems = false)
        {


            try
            {

                IEnumerable<AppointmentItem> items = await appointmentTable
                                        .ToEnumerableAsync();

                return new ObservableCollection<AppointmentItem>(items);

            }
            catch (MobileServiceInvalidOperationException msioe)
            {
                Debug.WriteLine(@"Invalid sync operation: {0}", msioe.Message);
            }
            catch (Exception e)
            {
                Debug.WriteLine(@"Sync error: {0}", e.Message);
            }
            return null;

        }

这是 dataManger 类中用于从数据库检索数据的代码。

目前我收到此错误:

Error CS1061 'Task>' does not contain a definition for 'Where' and no extension method 'Where' accepting a first argument of type 'Task>' could be found (are you missing a using directive or an assembly reference?

Answer 1

您的以下代码行:

var items = manager.GetAppointmentItemsAsync();

返回 Task显然不包含 Where这就是您收到错误的原因。

请将此行更改为:

var items = await manager.GetAppointmentItemsAsync();

然后你会得到一个 ObservableCollection<AppointmentItem> 类型的集合其中应该有 Where成员(member)。