Hey Android users, has this ever happened to you? You’re swiping through your open apps on the screen and when you get to the “Close all” button at the end, you tap without even thinking twice. But then it occurs to you that you’ve accidentally closed an app that you didn’t want to close. Now there is a way to prevent this infuriating event from taking place so that even if you tap on “Close all,” certain apps will remain open. This feature is available on the One UI interface used on many Samsung Galaxy phones.
By using this handy dandy feature, the app you’ve selected to lock can be accessed quickly and easily and won’t be shut even if you press on the “Close all” button. You can unlock the app by pressing on the lock icon that appears with the app in the multitasking screen. It’s a brilliant feature because every Android user has closed an app accidentally by tapping the “Close all” button.
On some Galaxy phones with One UI, you can lock an open app so that it isn’t accidentally shut
If you’ve ever wondered why iOS does not have a “Close all” button to clear open apps, here’s an interesting post from Apple’s own community support page that goes against the thoughts of obsessive phone users who always want to close their recently used apps. The post says closing apps does not improve performance or improve battery life. It also notes that Recent Apps are not running in the background. They are suspended
Source: Phone Arena