<!-- BEGIN COPY / PASTE -->
    class FlickerFreeWidget extends StatefulWidget {
      @override
      _FlickerFreeWidgetState createState() => _FlickerFreeWidgetState();
    }

    class _FlickerFreeWidgetState extends State<FlickerFreeWidget> with SingleTickerProviderStateMixin {
      late AnimationController _controller;
      late Animation<double> _animation;

      @override
      void initState() {
        super.initState();
        _controller = AnimationController(duration: const Duration(seconds: 1), vsync: this);
        _animation = Tween<double>(begin: 0, end: 1).animate(_controller)
          ..addListener(() {
            setState(() {});
          });
        _controller.repeat(reverse: true);
      }

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

      @override
      Widget build(BuildContext context) {
        return AnimatedBuilder(
          animation: _animation,
          builder: (context, child) {
            return Opacity(
              opacity: _animation.value,
              child: child,
            );
          },
          child: Container(
            width: 100,
            height: 100,
            color: Colors.blue,
          ),
        );
      }
    }
    <!-- END COPY / PASTE -->