37.4 The updating Callback Action

The updating callback action is like onChanged with the exception that it works with a special property wrapper named @GestureState. GestureState is like the standard @State property wrapper but is designed exclusively for use with gestures. The key difference, however, is that @GestureState properties automatically reset to the original state when the gesture ends. As such, the updating callback is ideal for storing transient state that is only needed while a gesture is being performed.

Each time an updating action is called, it is passed the following three arguments:

•DragGesture.Value instance containing information about the gesture.

•A reference to the @GestureState property to which the gesture has been bound.

•A Transaction object containing the current state of the animation corresponding to the gesture.

The DragGesture.Value instance is particularly useful and contains the following properties:

•...