startCountDown method
void
startCountDown()
启动倒计时定时器
Implementation
void startCountDown() {
if (isActive() || totalTime <= 0) return;
_timer = Timer.periodic(Duration(milliseconds: duration), (timer) {
var time = totalTime - duration;
totalTime = time;
if (time >= duration) {
_callback(time);
} else if (time == 0) {
_callback(time);
cancelTimer();
} else {
timer.cancel();
Future.delayed(Duration(milliseconds: time), () {
totalTime = 0;
cancelTimer();
});
}
});
}