Xamarin Forms Android & iOS Background Fetch

Question

Hello everyone, I want to request to my rest api in Xamarin forms , download data and comparing it another one if it suits conditions existing a local notification on background while application is closed. How can i do this with a interval like two minutes on background? I’m researching few days but i could not find anything. Anyone help me please ? Thanks :)

Leo Zhu - MSFT Leo Zhu - MSFT · Accepted Answer · 2020-02-04T04:23:54

Do you mean you want it works when your app is closed ? if yes,you could consider using Foreground Services

here is a simple sample for Android you could refer to,you could change the runnable according your needs.

1.Create a Service MyService.cs :

[Service(Enabled = true)]
public class MyService : Service
{
    private Handler handler;
    private Action runnable;
    private bool isStarted;
    private int DELAY_BETWEEN_LOG_MESSAGES = 5000;
    private int NOTIFICATION_SERVICE_ID = 1001;
    private int NOTIFICATION_AlARM_ID = 1002;
    private string NOTIFICATION_CHANNEL_ID = "1003";
    private string NOTIFICATION_CHANNEL_NAME = "MyChannel";
    public override void OnCreate()
    {
        base.OnCreate();

        handler = new Handler();

        //here is what you want to do always, i just want to push a notification every 5 seconds here
        runnable = new Action(() =>
        {
           if (isStarted)
            {
                DispatchNotificationThatAlarmIsGenerated("I'm running");
                handler.PostDelayed(runnable, DELAY_BETWEEN_LOG_MESSAGES);
            }
        });
    }

    public override StartCommandResult OnStartCommand(Intent intent, StartCommandFlags flags, int startId)
    {
        if (isStarted)
        {
            // service is already started
        }
        else
        {
            CreateNotificationChannel();
            DispatchNotificationThatServiceIsRunning();

            handler.PostDelayed(runnable, DELAY_BETWEEN_LOG_MESSAGES);
            isStarted = true;
        }
        return StartCommandResult.Sticky;
    }

    public override void OnTaskRemoved(Intent rootIntent)
    {
        //base.OnTaskRemoved(rootIntent);
    }

    public override IBinder OnBind(Intent intent)
    {
        // Return null because this is a pure started service. A hybrid service would return a binder that would
        // allow access to the GetFormattedStamp() method.
        return null;
    }

    public override void OnDestroy()
    {
        // Stop the handler.
        handler.RemoveCallbacks(runnable);

        // Remove the notification from the status bar.
        var notificationManager = (NotificationManager)GetSystemService(NotificationService);
        notificationManager.Cancel(NOTIFICATION_SERVICE_ID);

        isStarted = false;
        base.OnDestroy();
    }

    private void CreateNotificationChannel()
    {
        //Notification Channel
        NotificationChannel notificationChannel = new NotificationChannel(NOTIFICATION_CHANNEL_ID, NOTIFICATION_CHANNEL_NAME, NotificationImportance.Max);
        notificationChannel.EnableLights(true);
        notificationChannel.EnableVibration(true);
        notificationChannel.SetVibrationPattern(new long[] { 100, 200, 300, 400, 500, 400, 300, 200, 400 });


        NotificationManager notificationManager = (NotificationManager)this.GetSystemService(Context.NotificationService);
        notificationManager.CreateNotificationChannel(notificationChannel);
    }

    //start a foreground notification to keep alive 
    private void DispatchNotificationThatServiceIsRunning()
    {
        NotificationCompat.Builder builder = new NotificationCompat.Builder(this, NOTIFICATION_CHANNEL_ID)
               .SetDefaults((int)NotificationDefaults.All)
               .SetSmallIcon(Resource.Drawable.Icon)
               .SetVibrate(new long[] { 100, 200, 300, 400, 500, 400, 300, 200, 400 })
               .SetSound(null)
               .SetChannelId(NOTIFICATION_CHANNEL_ID)
               .SetPriority(NotificationCompat.PriorityDefault)
               .SetAutoCancel(false)
               .SetContentTitle("Mobile")
               .SetContentText("My service started")
               .SetOngoing(true);

        NotificationManagerCompat notificationManager = NotificationManagerCompat.From(this);
        StartForeground(NOTIFICATION_SERVICE_ID, builder.Build());
    }

    //every 5 seconds push a notificaition
    private void DispatchNotificationThatAlarmIsGenerated(string message)
    {
        var intent = new Intent(this, typeof(MainActivity));
        intent.AddFlags(ActivityFlags.ClearTop);
        var pendingIntent = PendingIntent.GetActivity(this, 0, intent, PendingIntentFlags.OneShot);

        Notification.Builder notificationBuilder = new Notification.Builder(this, NOTIFICATION_CHANNEL_ID)
            .SetSmallIcon(Resource.Drawable.Icon)
            .SetContentTitle("Alarm")
            .SetContentText(message)
            .SetAutoCancel(true)
            .SetContentIntent(pendingIntent);

        var notificationManager = (NotificationManager)GetSystemService(NotificationService);
        notificationManager.Notify(NOTIFICATION_AlARM_ID, notificationBuilder.Build());
    }
}

2.in your activity :

protected override void OnResume()
  {
      base.OnResume();
      StartMyRequestService();
  }
public void StartMyRequestService()
  {
      var serviceToStart = new Intent(this, typeof(MyService));
      StartService(serviceToStart);
  }

Xamarin Forms Android & iOS Background Fetch

1 Answers