如何從非異步方法調用異步方法？
[英]How to call async method from not async method?
問題描述
我正在以xamarin形式工作。 我試圖將Web服務綁定到日歷控件中。 請參閱以下日歷控件鏈接（XamForms.Controls.Calendar）。
https://github.com/rebeccaXam/XamForms.Controls.Calendar
第一個功能是創建7 * 6 = 42個標簽和按鈕，然后創建“ callWebService”方法來調用服務功能，這是一種異步方法，可從服務中獲取響應。
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)
{
}
}
第二個功能是“ callWebService”功能，我在列表收集對象中收集響應，然后調用“ ChangeClaendar”功能，該功能用於綁定標簽和按鈕文本並填充適當的顏色。
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)
{
}
}
第三個功能是“ 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)
{
}
}
問題是：
1.當我嘗試直接填寫標簽列表時，在“ Changecalendar”功能中
labels[i].Text = start.ToString(WeekdaysFormat);
它顯示了一個錯誤
“ UIKit一致性錯誤：您正在調用只能從UI線程調用的UIKit方法。” 所以為了消除這個錯誤，我寫了
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));
但它顯示我一個錯誤
System.ArgumentOutOfRangeException：索引超出范圍。 必須為非負數並且小於集合的大小。
2.如果將函數“ CallWebService”和“ ChangeCalendar”都一一放在“ FillCalendarWindow”中，則列表對象未綁定，控件從該函數中退出，直接調用ChangeCalendar函數，並給了我空引用對象。
4 個解決方案
解決方案1
3 2016-10-24 18:32:14
該問題未提供測試解決方案所需的完整源代碼。
回答有關在非異步方法中調用等待函數的問題。 您可以使用
CallWebService().Wait(optional timeout);
要么
CallWebService().GetAwaiter().GetResult();
您還應該更改函數定義
async void CallWebService(int Month, int Year)
至
async Task CallWebService(int Month, int Year);
正確處理異常和線程切換
如果可以在不阻塞的情況下調用CallWebService，那么您也可以
CallWebService(1,2).ContinueWith((task) =>
{
});
解決方案2
2 2016-10-25 17:44:10
我假設從UI線程調用了FillCalendarWindows（）方法，但是您不希望UI線程在外部操作GetResponseFromWebService.GetResponse發生時等待並凍結控件，這就是為什么要在內部進行異步調用的原因CallWebService（）。
我認為使用異步CallWebService的更好方法是使用“一路異步”，因此您必須將CallWebService上游的所有方法都更改為異步方法。 這具有額外的好處，您無需執行Device.BeginInvokeOnMainThread，因為async / await捕獲了調用方的同步上下文，因此將在UI線程上調用ChangeCalendar。
async void SomeEventHandler()
{
// called from the UI thread (or its equivalent in Xamarin)
await FillCalendarWindows();
}
protected async Task FillCalendarWindows()
{
try
{
//create 7*6 = 42 labels and buttons
await CallWebService(StartDate.Month, StartDate.Year);
}
catch (Exception e)
{
}
}
public async Task CallWebService(int Month, int Year)
{
try
{
await GetResponseFromWebService.GetResponse... ;
// .... same code as in your example
ChangeCalendar(....);
}
catch /*... */
{
}
}
protected void ChangeCalendar(int changes)
{
try
{
/* no need to do Device.BeginInvokeOnMainThread () so you can replace all that with normal calls*/
}
catch (Exception e)
{
/* ... */
}
}
不知道如何引發System.ArgumentOutOfRangeException，我無法在github上找到正確的代碼版本，因此無法調查該特定錯誤。 我的猜測是，您有多個線程正在修改“按鈕”集合，並且在調用Device.BeginInvokeOnMainThread時，您可能會發現該集合中的元素少於預期的數量。
TL; DR：始終使用async / await而不是以同步方式調用async方法，這應該使查找問題原因更加容易
解決方案3
2 已采納 2016-10-27 03:04:29
嘗試跟隨
protected async Task 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));
await CallWebService(StartDate.Month, StartDate.Year);
//CallServiceInNewTask(StartDate.Month, StartDate.Year);
//Device.BeginInvokeOnMainThread(() => await ChangeCalendar(CalandarChanges.All));
}
catch (Exception e)
{
}
}
您的Web服務應該像
public async Task 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)
{
await ChangeCalendar(CalandarChanges.All);
}
else
{
await ChangeCalendar(CalandarChanges.StartDate);
}
}
catch (WebException e)
{
}
}
而且您的ChnageCalender方法應該像
protected async Task 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)
{
}
}
解決方案4
1 2016-10-25 19:17:57
我從您的評論中至少看到2個問題
“ If（response.flag == true）（控制權從函數中消失了，直接調用ChangeCalendar（）－顯然是因為您沒有等待。
按鈕的數量（42）與標簽的數量（7）不同，因此，當您嘗試使用相同的“ i”去標簽[i]和按鈕[i]時，會得到標簽索引的ArgumentOutOfRangeException。 注意
if(r==0)，它將標簽數限制為7。for (int r = 0; r < 6; r++) { for (int c = 0; c < 7; c++) { if (r == 0) { labels.Add(new Label
如何從非異步 web API 調用異步方法
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