c# await in for loop

Question

I have a list of items that need to be updated if information is missing. However, I'm making a call to Google Location services to do that. I'm wondering how I can append the necessary Lat & Long information asynchronously if possible

my code

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

You can get multiple map points asynchronously with multiple tasks (notice that it requires to convert PullInfo() to 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));
}

If PullInfo() cannot be converted to async-await, you can force the thread to wait for the results, but it will block the current thread:

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));
}

Running example of this last code sample: https://ideone.com/0uXGlG

Answer 2

You just need to await the call to getting the data (notice how the await got moved from 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;
}

You're not modifying your SAPItems collection, just each individual item. Once you have the response, you can just update the then-current item in the loop.