lerpFrom method

@override Decoration? lerpFrom(Decoration? a, double t)

Linearly interpolates from another Decoration (which may be of a different class) to this.

When implementing this method in subclasses, return null if this class cannot interpolate from a. In that case, lerp will try a's lerpTo method instead. Classes should implement both lerpFrom and lerpTo.

Supporting interpolating from null is recommended as the Decoration.lerp method uses this as a fallback when two classes can't interpolate between each other.

The t argument represents position on the timeline, with 0.0 meaning that the interpolation has not started, returning a (or something equivalent to a), 1.0 meaning that the interpolation has finished, returning this (or something equivalent to this), and values in between meaning that the interpolation is at the relevant point on the timeline between a and this. 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 Decoration.lerp.

Implementation

@override
Decoration? lerpFrom(Decoration? a, double t) {
  if (a is UnderlineTabIndicator) {
    return GradientTabIndicator(
      borderSide: BorderSide.lerp(a.borderSide, borderSide, t),
      insets: EdgeInsetsGeometry.lerp(a.insets, insets, t)!,
    );
  }
  return super.lerpFrom(a, t);
}