createBallisticSimulation method
- @override
override
Returns a simulation for ballistic scrolling starting from the given position with the given velocity.
This is used by ScrollPositionWithSingleContext in the ScrollPositionWithSingleContext.goBallistic method. If the result is non-null, ScrollPositionWithSingleContext will begin a BallisticScrollActivity with the returned value. Otherwise, it will begin an idle activity instead.
The given position
is only valid during this method call. Do not keep a
reference to it to use later, as the values may update, may not update, or
may update to reflect an entirely unrelated scrollable.
Implementation
@override
Simulation createBallisticSimulation(ScrollMetrics position, double velocity) {
// If we're out of range and not headed back in range, defer to the parent
// ballistics, which should put us back in range at a page boundary.
if ((velocity <= 0.0 && position.pixels <= position.minScrollExtent) ||
(velocity >= 0.0 && position.pixels >= position.maxScrollExtent))
return super.createBallisticSimulation(position, velocity);
final Tolerance tolerance = this.tolerance;
final double target = _getTargetPixels(position, tolerance, velocity);
if (target != position.pixels)
return ScrollSpringSimulation(spring, position.pixels, target, velocity, tolerance: tolerance);
return null;
}