如何使用單個“await Task.WhenAll”簡化多個等待？

Question

我假設我必須在下面的代碼中使用Task.WhenAll但無法弄清楚它應該正確實現。

請幫忙。

 public async void UpdateData()
        {
            var month = (cbMonths.SelectedItem as MonthView).ID;
            var year = (cbYears.SelectedItem as YearView).ID;
            var deviceTypeID = (int)DeviceType;
            var calendar = await GetCalendar(month, year, deviceTypeID);
            var workTypes = await GetWorkTypes(); 

            if (calendar != null && workTypes != null) // Task.WhenAll ???
            {
                //...
            }
        }


 private async Task<List<WorkTypeItem>> GetWorkTypes()
        {
            try
            {
                HttpClient client = new HttpClient();

                var url = Properties.Settings.Default.ServerBaseUrl + @"/api/staff/WorkTypes";

                HttpResponseMessage response = await client.GetAsync(url);
                if (response.IsSuccessStatusCode)    // Check the response StatusCode
                {
                    var serSettings = new JsonSerializerSettings() { TypeNameHandling = TypeNameHandling.All };    
                    string responseBody = await response.Content.ReadAsStringAsync();

                    return JsonConvert.DeserializeObject<List<MSOCommon.WorkTypeItem>>(responseBody, serSettings); 
                }              
                else
                {
                    logger.Error(Properties.Resources.DATACannotGetWorkTypes);
                }
            }
            catch (Exception ex)
            {
                logger.Error(Properties.Resources.DATACannotGetWorkTypes + " " + ex.Message);
            }

            return null;
        }

Answer 1

如果您希望兩個任務同時執行，則不要await這些方法。 而是將他們的任務傳遞給變量並在Task.WhenAll調用它們

public async Task UpdateData() {
    var month = (cbMonths.SelectedItem as MonthView).ID;
    var year = (cbYears.SelectedItem as YearView).ID;
    var deviceTypeID = (int)DeviceType;
    var task1 = GetCalendar(month, year, deviceTypeID);
    var task2 = GetWorkTypes(); 

    await Task.WhenAll(task1, task2);

    var calendar = task1.Result;
    var workTypes = task2.Result;
}

另請注意，您應該避免使用async void方法。

Answer 2

var calendarTask = GetCalendar(month, year, deviceTypeID);
var workTypesTask = GetWorkTypes(); 

Task.WaitAll(calendarTask, workTypesTask);
var calendar = await calendarTask;
var workTypes = await workTypesTask;

要回答 @crazyGamer ，您這樣做的原因是為了讓兩個任務可以同時運行。 否則，您甚至在開始第二個任務之前就在等待第一個任務。 當然，如果他們相互依賴，那是一件好事。 否則，這會在 MP 系統上運行得更快。