C＃在for循環中等待

Question

如果缺少信息，我有一個需要更新的項目清單。 但是，我正在打電話給Google定位服務。 我想知道如何在可能的情況下異步添加必要的緯度和經度信息

我的代碼

public static void PullInfo()
{
   foreach (var item in SAPItems)
   {
        if(item.MDM_Latitude == null || item.MDM_Longitude == null)
        {
             var point = GetMapPoint(item.AddressLine1 + " " + item.FiveDigitZip);
             item.MDM_Latitude = point.Result.Latitude.ToString();
             item.MDM_Longitude = point.Result.Longitude.ToString();
        }                    
    }

    foreach(var item in SAPItems)
         Console.WriteLine(item.MDM_Latitude + " " + item.MDM_Longitude);
}

private static async Task<MapPoint> GetMapPoint(string add)
{
     var task = Task.Run(() => LocationService.GetLatLongFromAddress(add));
     return await task;
}

Answer 1

您可以通過多個任務異步獲取多個地圖點（注意，它需要將PullInfo()轉換為async-await）：

public static async Task PullInfo()
{
    // Create tasks to update items with latitude and longitude
    var tasks
        = SAPItems.Where(item => item.Latitude == null || item.Longitude == null)
            .Select(item =>
                GetMapPoint(item.AddressLine1 + " " + item.FiveDigitZip)
                    .ContinueWith(pointTask => {
                        item.MDM_Latitude = pointTask.Result.Latitude.ToString();
                        item.MDM_Longitude = pointTask.Result.Longitude.ToString();
                    }));

    // Non-blocking await for tasks completion
    await Task.WhenAll(tasks);

    // Iterate to append Lat and Long
    foreach(var item in SAPItems)
        Console.WriteLine(item.MDM_Latitude + " " + item.MDM_Longitude);
}

private static Task<MapPoint> GetMapPoint(string add)
{
     return Task.Run(() => LocationService.GetLatLongFromAddress(add));
}

如果PullInfo()無法轉換為async-await，則可以強制線程等待結果，但是它將阻塞當前線程：

public static void PullInfo()
{
    // Create tasks to update items with latitude and longitude
    var tasks
        = SAPItems.Where(item => item.Latitude == null || item.Longitude == null)
            .Select(item =>
                GetMapPoint(item.AddressLine1 + " " + item.FiveDigitZip)
                    .ContinueWith(pointTask => {
                        item.MDM_Latitude = pointTask.Result.Latitude.ToString();
                        item.MDM_Longitude = pointTask.Result.Longitude.ToString();
                    }));

    // Wait for tasks completion (it will block the current thread)
    Task.WaitAll(tasks.ToArray());

    // Iterate to append Lat and Long
    foreach(var item in SAPItems)
        Console.WriteLine(item.MDM_Latitude + " " + item.MDM_Longitude);
}

private static Task<MapPoint> GetMapPoint(string add)
{
     return Task.Run(() => LocationService.GetLatLongFromAddress(add));
}

最后一個代碼示例的運行示例： https : //ideone.com/0uXGlG

Answer 2

您只需要等待獲取數據的調用即可（注意await是如何從GetMapPoint ）：

public static async Task PullInfo()
{
   foreach (var item in SAPItems)
   {
        if(item.Latitude == null || item.Longitude == null)
        {
             var point = await GetMapPoint(item.AddressLine1 + " " + item.FiveDigitZip);

             item.MDM_Latitude = point.Latitude.ToString();
             item.MDM_Longitude = point.Longitude.ToString();
        }                    
    }

    foreach(var item in SAPItems)
         Console.WriteLine(item.MDM_Latitude + " " + item.MDM_Longitude);
}

private static Task<MapPoint> GetMapPoint(string add)
{
     var task = Task.Run(() => LocationService.GetLatLongFromAddress(add));
     return task;
}

您無需修改SAPItems集合，而只需修改每個單獨的項目。 獲得響應后，您只需更新循環中的當前項目即可。