startTimer method
void
startTimer()
Implementation
void startTimer() {
start.value = 30;
const oneSec = Duration(seconds: 1);
timer!.value = Timer.periodic(
oneSec,
(Timer timer) {
if (start.value == 0) {
timer.cancel();
} else {
if (start.value > 0) {
start.value--;
}
}
},
);
}