FlutterContainerTransformShrink

FlutterContainerTransformShrink.dart

class _PageAState extends State<PageA> {
  ...
  
  // A widget for page transition between the `pageA` and `pageB` after tapping the `FAB button`.
  Widget get _pageTransition {
    // Dismiss ripple widget if `_pageTransitionRect` is null.
    if (_pageTransitionRect == null) {
      return Container();
    }

    return AnimatedPositioned.fromRect(
      rect: _pageTransitionRect,
      duration: Duration(milliseconds: 300),
      child: Container(
        decoration: BoxDecoration(
          shape: BoxShape.circle,
          color: _FabButtonColor,
        ),
      ),
      onEnd: () {
        bool shouldNavigatePage = _pageTransitionRect != _fabButtonRect;
        if (shouldNavigatePage) {
          Navigator.push(
            context,
            FadeRouteBuilder(page: PageB()),
          ).then((_) {
            // Shrink back to the normal FAB button size.
            setState(() => _pageTransitionRect = _fabButtonRect);
          });
        } else {
          // Dismiss ripple widget after shrinking finishes.
          setState(() => _pageTransitionRect = null);
        }
      },
    );
  }
}