how to use timer.cancel() ? and it not work

[bobobo]

      setState(() {
        tweenIndex = (tweenIndex + 1) % colors.length;
      });
    });

and I add this code

floatingActionButton: FloatingActionButton(
        child: Icon(Icons.refresh),
        onPressed: (){
          timer.cancel();
        },
      ),

i try to cancel timer but it not work

[bobobo]

https://github.com/samarthagarwal/FlutterScreens/blob/master/lib/loaders/color_loader.dart#L69

[bobobo]

https://stackoverflow.com/questions/49087537/how-to-make-timer-periodic-cancel-itself-when-a-condition-is-reached
i found answer but i try it,but fail