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iosswiftuiapplicationdelegate

Will application Relaunch after app goes background

If I send my app to background by clicking the home button and wait a certain time (perhaps 1 or 2 hours).

What will happen if i tap on the app icon now?

Will the app relaunch or simply be brought from background to foreground?

Solution

  • Quick "prologue":

    Welcome to the wonderful world of stack overflow (SO), I myself am rather new here, but found it much friendlier to use welcome you anyway!

    Just in case you haven't: Before you ask a question please look around a bit on SO in case someone else has asked the same thing, but if you can't get your question answered from that, then you should of course ask your own question.

    Answer:

    This question has no definite answer, because it depends. When you tap the home button your app enters, as you've said, the background and is still running to a certain degree. However after done so, the apps life cycle is up to iOS (the devices operating system) to determine. iOS controls and checks memory and CPU usage (etc..) of the device, and if you start another activity while your app is in the background that makes the available memory and CPU etc of the device not sufficient, iOS will terminate any apps in the background to not waste those resources (or battery etc). If so your app will relaunch next time you tap on it.

    Although if you don't do anything performance heavy it is more likely that iOS keeps your device running in the background.

    I'm not sure about the exact conditions and such the iOS works on, but i would say its very likely your app will have gotten terminated and is relaunched after 1 or 2 hours "in the background". Additional conditions apply if the device is locked during that period.

    For proper documentation of this i would recommend reading Apples documentation for handling App State Transitions and/or the api for UIApplicationDelegate on apples developer website. Where you can see what the different methods in the AppDelegate does and how they interact.

    Edit (answer to comment):

    1. A way to relaunch the app everytime it goes into background?

      • Hm, yes, but also no. I'm not 100% sure about this (never encountered that "wish" before), but you can do this in your AppDelegate: (It will basically crash your app, but beware that apple does not encourage you to crash your own app anywhere). Doing this might stop the app from passing through apple store review process (i.e. your app might not be accepted to the App Store). 

        func applicationDidEnterBackground(_ application: UIApplication) {
     exit(0)
}

      • Check out the answer to these post for a bit more information: call exit(0) in iphone app , objc - Proper way to exit iPhone application?.

      • Personally I would recommend you to work around it and don't do this. Also remember that when your app will enter the background applicationWillResignActive will be called and when the user opens it again, applicationDidBecomeActive gets called so you can do a reload or something from there if you want to refresh any data.