Pressed back to exit Instagram, but instead, the feed refreshed—so I kept scrolling for another 15 minutes. Turns out, it's a clever design trick:

Instagram has a unique way of handling the back button, especially on Android devices, where pressing the back button on the feed does not close the app but instead refreshes the feed. This behavior is not default system behavior but is intentionally implemented by Instagram to improve user engagement and experience.

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1. Custom Intercepting of Back Button Presses (Android):

In Android, apps can override the system back button behavior by intercepting it inside activities or fragments using OnBackPressedCallback or onBackPressed().

Instead of allowing the app to close when the user presses the back button, Instagram triggers a refresh of the feed. Example:

val callback = object : OnBackPressedCallback(true) {
    override fun handleOnBackPressed() {
        refreshFeed() // Instead of closing, refresh the content
    }
}
requireActivity().onBackPressedDispatcher.addCallback(viewLifecycleOwner, callback)        

This prevents the app from closing and instead triggers a refresh of the Instagram feed.

2.Task Affinity & Back Stack Manipulation

Task Affinity allows Instagram to group different screens in a way that avoids the app being closed immediately.

Instead of exiting the app when the user is on the main feed, Instagram removes other fragments from the back stack and triggers a feed update.

3. How This Works in iOS :

iOS does not have a system-wide back button like Android but uses a gesture-based back navigation (swiping from the left).

Instagram handles this by controlling the UINavigationController stack:

If the user swipes back while on the feed, Instagram can trigger a refresh instead of taking them out of the app.