How to implement an Android Service in Xamarin.Forms

Question

I'm trying to periodically check with a web service if a new item has been added to a database. If there's a new item a listview that the user sees should be updated. I'm using PCL and I have accomplish it creating a new Task with a timer inside. But this only works if the app is open. I want to do the same when the app is closed so the user gets a notification when a new item is added remotely. I've been doing some research and I found andoid services, the info said that the service will continue, regardless of the app state, until you tell it to stop. But i haven't found many examples in how to implement it.

Here's the code that I had that works only when the app is opened:

 Task.Run(() =>
            {
                Device.StartTimer(TimeSpan.FromSeconds(secs), checkUpdates);
            });

  bool checkUpdates()
      {
        if (isOnline)
        {
            var lastUp= Application.Current.Properties["lastUpdate"] as string;

    //returns true if a new item is added
            if (service.newItem(DateTime.Parse(lastUp)))
            {
                var itm = service.getNewItem(DateTime.Parse(lastUp));

                Device.BeginInvokeOnMainThread(() =>
                {
                        notification.ShowNotification(itm.Title, 1000);
                        listView.Insert(0, itm);
                 }                        
                });                  
            }
            App.Current.Properties["lastUpdate"] = DateTime.Now.ToString();
        }
        return true;
    }

I'm trying to do the same with an Android service using dependency services, here's what I've got so far:

 public interface IService
    {
        void Start();
    }

  [Service]
    public class DependentService : Service, IService
    {
        public void Start()
        {
            var intent = new Intent(Android.App.Application.Context, typeof(DependentService));
            Android.App.Application.Context.StartService(intent);
        }

        public override IBinder OnBind(Intent intent)
        {
            return null;
        }

        public override StartCommandResult OnStartCommand(Intent intent, StartCommandFlags flags, int startId)
        {
            // From shared code or in your PCL


            return StartCommandResult.NotSticky;
        }
    }

The problem is that I don't know how to implement the code that I had in the timer to the service, can someone please help?

Answer 1

For what you want to achieve, you should probably look at the AlarmManager

Have a look at this StackOverflow post , where there's an example for one and maybe this one as well. The second one is Java but it might give you an idea of what you might deal with

EDIT:

You might also want to have a look at these Xamarin.Android documents around Services and BroadcastReceivers , to get better understanding with what you're dealing