What is addListener in Dart?

addListener method Null safety Adds a listener callback that is called whenever a new concrete ImageInfo object is available or an error is reported . If a concrete image is already available, or if an error has been already reported, this object will notify the listener synchronously.

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What is GestureDetector?

android.view.GestureDetector. Detects various gestures and events using the supplied MotionEvent s . The OnGestureListener callback will notify users when a particular motion event has occurred. This class should only be used with MotionEvent s reported via touch (don’t use for trackball events).

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