+
                controller =

19

+
                    AnimationController(duration: const Duration(seconds: 2), vsync: this);

20

+
                animation = Tween<double>(begin: 0, end: 300).animate(controller)

21

+
                  ..addListener(() {

22

+
                    setState(() {

23

+
                      // The state that has changed here is the animation object’s value.

24

+
                    });

25

+
                  });

26

+
                controller.forward();

27

+
              }

28

12
29