public class Service
{
    HttpClient client;

    public Service()
    {
        client = new HttpClient();
        client.MaxResponseContentBufferSize = 256000;
    }

    public async Task<ObservableCollection<TodoItem>> DataAsync(int id, string dist)
    {
        string Json = "https://api...." + id + "&dist=" + dist;
        try
        {
            var response = await client.GetAsync(Json);
            if (response.IsSuccessStatusCode)
            {
                var content = await response.Content.ReadAsStringAsync();
                ObservableCollection<TodoItem> stations = JsonConvert.DeserializeObject<ObservableCollection<TodoItem>>(content);
                Debug.WriteLine(content);
                return stations;
            }
            else
            {
                return null;
            }
        }
        catch (HttpRequestException e)
        {
            Debug.WriteLine("nException Caught!");
            Debug.WriteLine("Message :{0} ", e.Message);
            return null;
        }
    }
}

public async Task Get()
    {
        var PinDataAsync = await _Service.DataAsync(Item.id, "5000");

        try
        {
            foreach (var i in PinDataAsync)
            {
                var pin = new Pin
                {
                    Type = PinType.Place,
                    Position = new Position(i.lat, i.lon),
                    Label = i.name
                };
                Map.Pins.Add(pin);
            }
        }
        catch (Exception err)
        {
            Debug.WriteLine("Error {0}", err);
        }
    }