resetActivity method Null safety
override
Called by the ScrollActivityDelegate when it has changed type (for example, when changing from an Android-style scroll position to an iOS-style scroll position). If this activity can differ between the two modes, then it should tell the position to restart that activity appropriately.
For example, BallisticScrollActivity's implementation calls ScrollActivityDelegate.goBallistic.
Implementation
@override
void resetActivity() {
delegate.goBallistic(velocity);
}