onstart

onStart is a lifecycle callback used in several software frameworks to signal that a component is about to become visible or active. In Android, onStart is a method in the Activity and Fragment lifecycles. It is called after onCreate and when the activity or fragment becomes visible to the user, preceding onResume, which indicates the component has focus. If an activity has been stopped, onRestart precedes onStart when it is being brought back to the screen. The counterpart to onStart is onStop, which is called when the component is no longer visible to the user. Typical use during onStart includes registering listeners or services that should be active while the UI is visible, starting lightweight animations, or initializing resources that need to be present for the visible portion of the UI. Heavy initialization or long-running tasks should generally be deferred to onResume or to background work.

In fragments, onStart serves a similar purpose: it is invoked when the fragment becomes visible, and onStop when it is no longer visible. Not all frameworks expose an onStart method; in those cases the analogous hook varies, but the concept remains the same: a transition point when the component starts being presented to the user.

Because lifecycle methods can be invoked multiple times during an app's life, implementations typically avoid assuming one-time initialization inside onStart and instead manage resources and state accordingly, releasing or re-acquiring resources in onStop.