onRestart

onRestart is a lifecycle callback in Android's Activity class. It is invoked when an activity is restarting after being stopped, not when it is created for the first time.

The method is called after onStop() and before onStart() as the activity transitions from the stopped state back to the started state. This typically occurs when the user navigates back to the activity or the system restores the activity after reclaiming resources. If the activity is merely being created from scratch, onRestart is not involved.

Usage of onRestart is optional. Developers override onRestart() to reinitialize resources or refresh UI elements that may have been released or paused during onStop. The default implementation is empty, so any behavior is implemented by the programmer. A common pattern is to call super.onRestart() and then perform any necessary restoration, such as re-binding to services, restarting animations, or updating displayed data.

Relation to other lifecycle methods: onRestart is followed by onStart and then onResume, leading back to user interaction. It is distinct from onCreate, which runs only when the activity is created for the first time. If the activity is destroyed while stopped and then recreated, onRestart is not invoked; instead, a new instance goes through onCreate, onStart, and onResume.

Notes: onRestart provides a targeted hook for state restoration after a stop, but its necessity depends on the specific resource and UI management needs of the activity.