How to let the app run at background even if it is closed ?!

If you specifically want to make an app that pops up messages at specific times (like reminders,) you want to look up Local Notifications.

If you want something else to run in the background, you may be out of luck, as Apple only allows a select few types of apps to run in the background. (off the top of my head, I think apple allows geo-fence notifications, local notifications, push notifications, VOIP, and music streaming tasks to run in the background. I might be missing one or two.)

Here's a good apple doc to look at:
https://developer.apple.com/library...cationsFlow/ManagingYourApplicationsFlow.html

The whole doc is pretty relevant to what you want, but you'll especially want to focus on the last section called "Background Execution and Multitasking". They have lists of the types of activities your app is allowed to do in the background.

 

Hmm... I suppose you're correct, there is a difference, or else Sparrow could have just used push notifications as they wanted in their app.

 

Opening Push Notifications will open your view, and you can send a dictionary with your Push Notification, which you can use to open a specific view right of the bat (even though you're newly opening the application).