a scrollphysics that allows the user to pull the content down so that it is within reach from the bottom of the phone

_ExtraScrollPhysics.dart

//a scrollphysics that allows the user to pull the content down so that it is within reach from the bottom of the phone
class _ExtraScrollPhysics extends AlwaysScrollableScrollPhysics {
  final double extra;
  _ExtraScrollPhysics({this.reach, ScrollPhysics parent})
      : super(parent: parent);
  ScrollMetrics expandScrollMetrics(ScrollMetrics extant) {
    return FixedScrollMetrics(
      pixels: extant.pixels,
      axisDirection: extant.axisDirection,
      minScrollExtent:
          min(extant.minScrollExtent, -extra),
      maxScrollExtent: extant.maxScrollExtent,
      viewportDimension: extant.viewportDimension,
    );
  }

  _ExtraScrollPhysics applyTo(ScrollPhysics ancestor) {
    return _ExtraScrollPhysics(parent: buildParent(ancestor), reach: reach);
  }

  @override
  double applyPhysicsToUserOffset(ScrollMetrics position, double offset) {
    return super
        .applyPhysicsToUserOffset(expandScrollMetrics(position), offset);
  }

  @override
  bool shouldAcceptUserOffset(ScrollMetrics position) {
    return super.shouldAcceptUserOffset(expandScrollMetrics(position));
  }

  @override
  double adjustPositionForNewDimensions({
    ScrollMetrics oldPosition,
    ScrollMetrics newPosition,
    bool isScrolling,
    double velocity,
  }) {
    return super.adjustPositionForNewDimensions(
        oldPosition: expandScrollMetrics(oldPosition),
        newPosition: expandScrollMetrics(newPosition),
        isScrolling: isScrolling,
        velocity: velocity);
  }

  @override
  double applyBoundaryConditions(ScrollMetrics position, double value) {
    // return min(
    //   value - minAllowance,
    // );
    return super.applyBoundaryConditions(
      expandScrollMetrics(position),
      value,
    );
  }

  @override
  Simulation createBallisticSimulation(
      ScrollMetrics position, double velocity) {
    return super
        .createBallisticSimulation(expandScrollMetrics(position), velocity);
  }
}