Working in the background

I’ve presumed htat you’re talking about iOS here. Lemme know if that’s different.

Is there any way for part of the app to always run in the background

Not in general. See my iOS Background Execution Limits post.

so when the user opens the app it will be updated.

But that may be possible, using a variety of different techniques. Please read through the above post and, if you have follow-up questions, post back here with information about your requirements.

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—
Quinn “The Eskimo!” @ Developer Technical Support @ Apple
let myEmail = "eskimo" + "1" + "@" + "apple.com"