safety -- late initialization error // FLUTTER

Question

I have an error in the code because of safety in Flutter and I have tried to solve it with the declaration of variables using LATE.<br /

But it appears antother one when I try to build it:

Error

This is my code:

class AnimacionesPage extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Center(
        child: CuadradoAnimado(),
      ),
    );
  }
}

class CuadradoAnimado extends StatefulWidget {
  @override
  _CuadradoAnimadoState createState() => _CuadradoAnimadoState();
}

class _CuadradoAnimadoState extends State<CuadradoAnimado>
    with SingleTickerProviderStateMixin {
  late AnimationController controller;
  late Animation<double> rotacion;

@override
  void initState() {
    controller = new AnimationController(
        vsync: this, duration: Duration(milliseconds: 4000));

    rotacion = Tween(begin: 0.0, end: 2 * Math.pi)
        .animate(CurvedAnimation(parent: controller, curve: Curves.easeOut));

 @override
  Widget build(BuildContext context) {
    // Play / Reproducción
    controller.forward();

    return AnimatedBuilder(
      animation: controller,
      child: _Rectangulo(),

Answer 1

try this

     class _CuadradoAnimadoState extends State<CuadradoAnimado>
                with SingleTickerProviderStateMixin {
              AnimationController? controller;
              Animation<double>? rotacion;
            
            @override
              void initState() {
                controller = new AnimationController(
                    vsync: this, duration: Duration(milliseconds: 4000));
            
                rotacion = Tween(begin: 0.0, end: 2 * Math.pi)
                    .animate(CurvedAnimation(parent: controller, curve: Curves.easeOut));
             controller.forward();
setState((){});
    }
             @override
              Widget build(BuildContext context) {
                // Play / Reproducción
               
            
                return controller==null && rotacion==null ? CircularProgressIndicator.adaptive():  AnimatedBuilder(
                  animation: controller!,
                  child: _Rectangulo());