iOS - automatically open app from background

Question

Is it possible to reopen the app from background mode in some way? For example, if the app in background is checking the server for some flag, and then when triggered, it will automatically go to foreground?

If not, can i display a message and play sound for the user to request app reopen?

How does for example WhatsApp achieve this?

Answer 1

It's not possible to automatically open the app, meaning display the app to the user.

However it is possible using Push Notifications to have your app opened in the background so that it can perform a short task. This is achieved by creating a push notification with the content-available field.

If your server sends push notifications to a user’s device when new content is available for your app, you can ask the system to run your app in the background so that it can begin downloading the new content right away. The intent of this background mode is to minimize the amount of time that elapses between when a user sees a push notification and when your app is able to able to display the associated content. Apps are typically woken up at roughly the same time that the user sees the notification but that still gives you more time than you might have otherwise.

To support this background mode, enable the Remote notifications option from the Background modes section of the Capabilities tab in your Xcode project. (You can also enable this support by including the UIBackgroundModes key with the remote-notification value in your app’s Info.plist file.)

For a push notification to trigger a download operation, the notification’s payload must include the content-available key with its value set to 1. When that key is present, the system wakes the app in the background (or launches it into the background) and calls the app delegate’s application:didReceiveRemoteNotification:fetchCompletionHandler: method. Your implementation of that method should download the relevant content and integrate it into your app.

When downloading any content, it is recommended that you use the NSURLSession class to initiate and manage your downloads. For information about how to use this class to manage upload and download tasks, see URL Loading System Programming Guide.

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can i display a message and play sound for the user to request app reopen?

Yes, you can just use a Local Notification or a Push Notification