CODE EXAMPLE FOR TYPESCRIPT

flutter animate size change

AnimatedSize(
  vsync: this,
  duration: Duration(milliseconds: 150),
  curve: Curves.fastOutSlowIn,
  child: Container(
    child: Container(
      child: !_isExpanded
          ? null
          : FadeTransition(opacity: animationFade, child: widget.child),
    ),
  ),
);