lerpTo method Null safety

  1. @override
ShapeBorder? lerpTo(
  1. ShapeBorder? b,
  2. double t
)
override

Linearly interpolates from this to another ShapeBorder (possibly of another class).

This is called if b's lerpTo did not know how to handle this class.

When implementing this method in subclasses, return null if this class cannot interpolate from b. In that case, lerp will apply a default behavior instead. If b is null, this must not return null.

The base class implementation handles the case of b being null by deferring to scale.

The t argument represents position on the timeline, with 0.0 meaning that the interpolation has not started, returning this (or something equivalent to this), 1.0 meaning that the interpolation has finished, returning b (or something equivalent to b), and values in between meaning that the interpolation is at the relevant point on the timeline between this and b. The interpolation can be extrapolated beyond 0.0 and 1.0, so negative values and values greater than 1.0 are valid (and can easily be generated by curves such as Curves.elasticInOut).

Values for t are usually obtained from an Animation<double>, such as an AnimationController.

Instead of calling this directly, use ShapeBorder.lerp.

Implementation

@override
ShapeBorder? lerpTo(ShapeBorder? b, double t) {
  assert(t != null);
  if (b is StadiumBorder) {
    return StadiumBorder(side: BorderSide.lerp(side, b.side, t));
  }
  if (b is CircleBorder) {
    return _StadiumToCircleBorder(
      side: BorderSide.lerp(side, b.side, t),
      circleness: t,
      eccentricity: b.eccentricity,
    );
  }
  if (b is RoundedRectangleBorder) {
    return _StadiumToRoundedRectangleBorder(
      side: BorderSide.lerp(side, b.side, t),
      borderRadius: b.borderRadius as BorderRadius,
      rectness: t,
    );
  }
  return super.lerpTo(b, t);
}