Stateful Animation

main.dart

import 'package:flutter/material.dart';

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      showPerformanceOverlay: true,
      title: 'Flutter Demo',
      theme: ThemeData(
        brightness: Brightness.dark,
        primarySwatch: Colors.blue,
      ),
      home: MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyHomePage extends StatelessWidget {
  final String title;
  MyHomePage({this.title});
  @override
  Widget build(BuildContext context) {
    return AnimatedBackground();
  }
}

class AnimatedBackground extends StatefulWidget {
  const AnimatedBackground({
    Key key,
  }) : super(key: key);

  @override
  AnimatedBackgroundState createState() {
    return new AnimatedBackgroundState();
  }
}

class AnimatedBackgroundState extends State<AnimatedBackground>
    with SingleTickerProviderStateMixin {
  Animation animation;
  AnimationController animationController;

  @override
  void dispose() {
    // TODO: implement dispose
    super.dispose();
    animationController.dispose();
  }

  @override
  void initState() {
    // TODO: implement initState
    super.initState();

    animationController =
        AnimationController(vsync: this, duration: Duration(seconds: 2));
    animation = Tween(begin: -1, end: 0).animate( //This is the problem, I use -1.0 & 0.0 instead
        CurvedAnimation(curve: Curves.easeInOut, parent: animationController));

    animationController.repeat();
  }

  @override
  Widget build(BuildContext context) {
    final double width = MediaQuery.of(context).size.width;
    return AnimatedBuilder(
        animation: animationController,
        builder: (context, _) => Scaffold(
            body: Transform(
                transform: Matrix4.translationValues(
                    animation.value * width, 0.0, 0.0),
                child: Center(child: Text("Dash")))));
  }
}