applyBoundaryConditions method

  1. @protected
double applyBoundaryConditions (double value)
@protected

Returns the overscroll by applying the boundary conditions.

If the given value is in bounds, returns 0.0. Otherwise, returns the amount of value that cannot be applied to pixels as a result of the boundary conditions. If the physics allow out-of-bounds scrolling, this method always returns 0.0.

The default implementation defers to the physics object's ScrollPhysics.applyBoundaryConditions.

Implementation 

@protected
double applyBoundaryConditions(double value) {
  final double result = physics.applyBoundaryConditions(this, value);
  assert(() {
    final double delta = value - pixels;
    if (result.abs() > delta.abs()) {
      throw FlutterError(
        '${physics.runtimeType}.applyBoundaryConditions returned invalid overscroll value.\n'
        'The method was called to consider a change from $pixels to $value, which is a '
        'delta of ${delta.toStringAsFixed(1)} units. However, it returned an overscroll of '
        '${result.toStringAsFixed(1)} units, which has a greater magnitude than the delta. '
        'The applyBoundaryConditions method is only supposed to reduce the possible range '
        'of movement, not increase it.\n'
        'The scroll extents are $minScrollExtent .. $maxScrollExtent, and the '
        'viewport dimension is $viewportDimension.'
      );
    }
    return true;
  }());
  return result;
}