Managing camera lifecycle in Vision Camera

WHAT THIS TESTS Whether you treat the camera as a costly hardware resource whose active session must be tied to whether the user is actually looking at it.

A GOOD ANSWER COVERS Vision Camera's Camera component takes an isActive boolean prop that controls whether the underlying capture session is running. The idiomatic pattern is to compute isActive from two signals: navigation focus and app foreground state. You use useIsFocused from React Navigation so the camera is active only on the focused screen, not on screens stacked behind it, and you read AppState so the session pauses when the app goes to the background. Combining them, isActive equals isFocused and appState is active. When isActive flips to false, Vision Camera stops streaming frames and powers down the session, eliminating battery drain, and flips back on quickly when the screen is refocused. This is preferable to fully unmounting the camera, which is slower to reinitialize and can drop the preview. You also pause or gate the frame processor or code scanner so QR decoding does not run while inactive.

COMMON WRONG ANSWERS Leaving isActive permanently true, so the camera keeps running on background screens and drains battery. Relying only on mounting and unmounting, which causes a slow, flickery resume. Forgetting AppState, so the camera stays live when the app is backgrounded. Running the frame processor even when isActive is false. Not handling the permission and device-not-ready states.

LIKELY FOLLOW-UPS Why is toggling isActive better than unmounting, how do frame processors interact with the lifecycle, how do you handle the camera on app resume, and how do you throttle QR detection to save CPU.

ONE CONCRETE EXAMPLE const isFocused = useIsFocused(); plus an appState piece of state. const isActive = isFocused && appState === 'active'. You pass isActive to the Camera. Navigating away from the scanner sets isFocused false, so the session pauses; returning re-focuses and the preview resumes almost instantly. Backgrounding the app sets appState inactive, pausing the camera without unmounting the screen.