how to animate collapse elements in flutter

Question

How can i expand and collapse widget when user taps on different widget ( sibling or parent ) with animation ?

new Column(
    children: [
            


        

Answer 1

If you want to collapse a widget to zero height or zero width that has a child that overflow when collapsed, I would recommend SizeTransition or ScaleTransition.

Here is an example of the ScaleTransition widget being used to collapse the container for the four black buttons and status text. My ExpandedSection widget is used with a column to get the following structure.

An example of a Widget that use animation with the SizeTransition widget:

class ExpandedSection extends StatefulWidget {

  final Widget child;
  final bool expand;
  ExpandedSection({this.expand = false, this.child});

  @override
  _ExpandedSectionState createState() => _ExpandedSectionState();
}

class _ExpandedSectionState extends State with SingleTickerProviderStateMixin {
  AnimationController expandController;
  Animation animation; 

  @override
  void initState() {
    super.initState();
    prepareAnimations();
    _runExpandCheck();
  }

  ///Setting up the animation
  void prepareAnimations() {
    expandController = AnimationController(
      vsync: this,
      duration: Duration(milliseconds: 500)
    );
    animation = CurvedAnimation(
      parent: expandController,
      curve: Curves.fastOutSlowIn,
    );
  }

  void _runExpandCheck() {
    if(widget.expand) {
      expandController.forward();
    }
    else {
      expandController.reverse();
    }
  }

  @override
  void didUpdateWidget(ExpandedSection oldWidget) {
    super.didUpdateWidget(oldWidget);
    _runExpandCheck();
  }

  @override
  void dispose() {
    expandController.dispose();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return SizeTransition(
      axisAlignment: 1.0,
      sizeFactor: animation,
      child: widget.child
    );
  }
}

AnimatedContainer also works but Flutter can complain about overflow if the child is not resizable to zero width or zero height.