c# - 如何从非异步方法调用异步方法？

Question

我在 xamarin 表单中工作。我正在尝试在日历控件中绑定(bind) Web 服务。请参阅以下日历控件链接 (XamForms.Controls.Calendar)。

https://github.com/rebeccaXam/XamForms.Controls.Calendar

第一个函数 是创建 7*6=42 个标签和按钮，然后使用“callWebService”方法调用服务函数，这是从服务获取响应的异步方法。

protected void FillCalendarWindows()
        {
            try
            {
                for (int r = 0; r < 6; r++)
                {
                    for (int c = 0; c < 7; c++)
                    {
                        if (r == 0)
                        {
                            labels.Add(new Label
                            {
                                HorizontalOptions = LayoutOptions.Center,
                                VerticalOptions = LayoutOptions.Center,
                                TextColor = Color.Black,
                                FontSize = 18,
                                FontAttributes = FontAttributes.Bold
                            });
                            DayLabels.Children.Add(labels.Last(), c, r);
                        }
                        buttons.Add(new CalendarButton
                        {
                            BorderRadius = 0,
                            BorderWidth = BorderWidth,
                            BorderColor = BorderColor,
                            FontSize = DatesFontSize,
                            BackgroundColor = DatesBackgroundColor,
                            HorizontalOptions = LayoutOptions.FillAndExpand,
                            VerticalOptions = LayoutOptions.FillAndExpand
                        });
                        buttons.Last().Clicked += DateClickedEvent;
                        MainCalendar.Children.Add(buttons.Last(), c, r);
                    }
                }
                flag = 1;
                //Device.BeginInvokeOnMainThread(() => CallWebService(StartDate.Month, StartDate.Year));
                CallWebService(StartDate.Month, StartDate.Year);
                //CallServiceInNewTask(StartDate.Month, StartDate.Year);
                //Device.BeginInvokeOnMainThread(() => ChangeCalendar(CalandarChanges.All));

            }
            catch (Exception e)
            {

            }
        }

第二个函数 是“callWebService”函数，我在列表集合对象中收集响应，然后调用“ChangeClaendar”函数，该函数用于绑定(bind)标签和按钮文本并填充适当的颜色。

public async void CallWebService(int Month, int Year)
        {
            try
            {
                var response = await GetResponseFromWebService.GetResponse<ServiceClasses.RootObject_AttendanceTable>(ServiceURL.GetAttendanceTableList + "Month=" + Month + "&Year=" + Year + "&EmpCd=" + _empCode);
                if (response.Flag == true)
                {
                    if (ListObjAttendanceTblList == null)
                    {
                        ListObjAttendanceTblList = new List<LstAttendanceDtl>();
                    }
                    for (int i = 0; i < response.lstAttendanceDtl.Count; i++)
                    {
                        var objAttendanceTableList = new LstAttendanceDtl();

                        objAttendanceTableList.AttendanceDt = response.lstAttendanceDtl[i].AttendanceDt;
                        objAttendanceTableList.EarlyDeparture = response.lstAttendanceDtl[i].EarlyDeparture;
                        objAttendanceTableList.InTime = response.lstAttendanceDtl[i].EarlyDeparture;
                        objAttendanceTableList.LateArrival = response.lstAttendanceDtl[i].EarlyDeparture;
                        objAttendanceTableList.OutTime = response.lstAttendanceDtl[i].OutTime;
                        objAttendanceTableList.OverTime = response.lstAttendanceDtl[i].OverTime;
                        objAttendanceTableList.Reason = response.lstAttendanceDtl[i].Reason;
                        objAttendanceTableList.Remark = response.lstAttendanceDtl[i].Remark;
                        objAttendanceTableList.Shift = response.lstAttendanceDtl[i].Shift;
                        objAttendanceTableList.WorkingHrs = response.lstAttendanceDtl[i].WorkingHrs;

                        ListObjAttendanceTblList.Add(objAttendanceTableList);
                    }
                }
                else
                {
                }
                if (flag == 1)
                {
                    ChangeCalendar(CalandarChanges.All);
                }
                else
                {
                    ChangeCalendar(CalandarChanges.StartDate);
                }
            }
            catch (WebException e)
            {

            }
        } 

第三个功能是“ChangeCalendar”

protected void ChangeCalendar(CalandarChanges changes)
        {
            try
            {
                if (changes.HasFlag(CalandarChanges.StartDate))
                {
                    Device.BeginInvokeOnMainThread(() => CenterLabel.Text = StartDate.ToString(TitleLabelFormat));
                }
                var start = CalendarStartDate;
                var beginOfMonth = false;
                var endOfMonth = false;
                for (int i = 0; i < buttons.Count; i++)
                {
                    endOfMonth |= beginOfMonth && start.Day == 1;
                    beginOfMonth |= start.Day == 1;

                    LstAttendanceDtl objAttendanceDtl = ListObjAttendanceTblList.Find(s => s.AttendanceDt.Equals(start.Date.ToString("dd/MM/yyyy")));
                    string remarks = string.Empty;

                    if (i < 7 && WeekdaysShow && changes.HasFlag(CalandarChanges.StartDay))
                    {
                        Device.BeginInvokeOnMainThread(() => labels[i].Text = start.ToString(WeekdaysFormat));
                        //labels[i].Text = start.ToString(WeekdaysFormat);
                        //DateTime d = Convert.ToDateTime(objAttendanceDtl.AttendanceDt).Date; 
                    }
                    if (changes.HasFlag(CalandarChanges.All))
                    {
                        Device.BeginInvokeOnMainThread(()=>buttons[i].Text = string.Format("{0}", start.Day));
                        //buttons[i].Text = string.Format("{0}", start.Day);
                    }
                    else
                    {
                        Device.BeginInvokeOnMainThread(() => buttons[i].TextWithoutMeasure = string.Format("{0}", start.Day));
                    }

                    buttons[i].Date = start;
                    var isInsideMonth = beginOfMonth && !endOfMonth;
                    if (objAttendanceDtl != null)
                    {
                        remarks = objAttendanceDtl.Remark;

                        if ((remarks.ToLower()).Trim() == stringFullDay.ToLower().Trim())
                        {
                            SetButtonPresent(buttons[i], isInsideMonth);
                        }
                        else if (remarks.ToLower().Trim() == stringAbsent.ToLower().Trim())
                        {
                            SetButtonAbsent(buttons[i], isInsideMonth);
                        }
                        else if (remarks.ToLower().Trim() == stringWeekOff.ToLower().Trim())
                        {
                            SetButtonWeekendMood(buttons[i], isInsideMonth);
                        }
                        else if (remarks.ToLower().Trim() == stringHolidays.ToLower().Trim())
                        {
                            SetButtonHolidays(buttons[i], isInsideMonth);
                        }
                        else if (remarks.ToLower().Trim() == stringSecondhalfAbsent.ToLower().Trim() ||
                            remarks.ToLower().Trim() == stringFirsthalfAbsent.ToLower().Trim())
                        {
                            SetButtonHalfDayMood(buttons[i], isInsideMonth);
                        }
                        else
                        {
                            SetButtonDisabled(buttons[i]);
                        }
                    }
                    else
                    {
                        SetButtonOutSideMonth(buttons[i]);
                    }
                    SpecialDate sd = null;
                    if (SpecialDates != null)
                    {
                        sd = SpecialDates.FirstOrDefault(s => s.Date.Date == start.Date);
                    }

                    if (sd != null)
                    {
                        SetButtonSpecial(buttons[i], sd);
                    }
                    else if (SelectedDate.HasValue && start.Date == SelectedDate.Value.Date)
                    {
                        SetButtonSelected(buttons[i], isInsideMonth);
                    }
                    start = start.AddDays(1);
                }
            }
            catch (Exception e)
            {

            }
        }

问题是:

1. 在“Changecalendar”功能中，当我尝试直接填写标签列表时

labels[i].Text = start.ToString(WeekdaysFormat);

显示错误

“UIKit 一致性错误:您正在调用只能从 UI 线程调用的 UIKit 方法。” 所以为了消除这个错误，我写了

Device.BeginInvokeOnMainThread(() => labels[i].Text = start.ToString(WeekdaysFormat));

Device.BeginInvokeOnMainThread(()=>buttons[i].Text = string.Format("{0}", start.Day));

Device.BeginInvokeOnMainThread(() => buttons[i].TextWithoutMeasure = string.Format("{0}", start.Day));

但它向我显示错误

System.ArgumentOutOfRangeException:索引超出范围。必须为非负数且小于集合的大小。

2. 如果我将函数“CallWebService”和“ChangeCalendar”一个接一个地放在“FillCalendarWindow”中，则列表对象未绑定(bind)并且控制从函数中出来并直接调用 ChangeCalendar 函数并给我空引用对象。

Answer 1

问题没有提供测试解决方案所需的完整源代码。

回答您关于在非异步方法中调用可等待函数的问题。你可以使用

CallWebService().Wait(optional timeout); 

或

CallWebService().GetAwaiter().GetResult(); 

你还应该改变你的函数定义

async void CallWebService(int Month, int Year)

到

async Task CallWebService(int Month, int Year);

正确处理异常和线程切换

如果您可以在不阻塞的情况下调用 CallWebService，那么您也可以这样做

CallWebService(1,2).ContinueWith((task) =>
{

});