Stopwatch don't decrease time - flutter

Question

I'm trying to make a timer that can be instantiated by any class, but I'm having problems with the TimerWidget class, since its value does not reduce in startTimer(). When called, the class has the same attributes as the TimerWidget class, and as described in the parameter, the timer starts counting with the required value. The errors say that the operator '<' and '-' do not belong to the type Time.
Any suggestions? Tips? I'm new to flutter.
import 'package:flutter/material.dart';
import 'dart:async';
class TimerWidget extends StatefulWidget {
final int hours; // 1 hour:
final int minutes; // 60
final int seconds; // 3.600
final int millisecond; // 3.600.000
final int microsecond; // 3.600.000.000
final int nanosecond; // 3.600.000.000.000
TimerWidget({
this.hours,
this.minutes,
u/required this.seconds,
this.millisecond,
this.microsecond,
this.nanosecond,
});
#override
_TimerWidgetState createState() => _TimerWidgetState();
}
class _TimerWidgetState extends State<TimerWidget> {
Timer _timer;
var start = TimerWidget(seconds: 30);
void startTimer() {
const oneSec = const Duration(seconds: 1);
_timer = new Timer.periodic(
oneSec,
(Timer timer) => setState(
() {
if (start < 1) {
timer.cancel();
} else {
start = start - 1;
}
},
),
);
}
#override
void dispose() {
_timer.cancel();
super.dispose();
}
Widget build(BuildContext context) {
return new Scaffold(
body: Column(
children: <Widget>[
RaisedButton(
onPressed: () {
startTimer();
},
child: Text("start"),
),
Text("$start")
],
),
);
}
}

Answer 1

You can copy paste run full code below
You can use var start = 30; not var start = TimerWidget(seconds: 30);
working demo
full code
import 'package:flutter/material.dart';
import 'dart:async';
class TimerWidget extends StatefulWidget {
final int hours; // 1 hour:
final int minutes; // 60
final int seconds; // 3.600
final int millisecond; // 3.600.000
final int microsecond; // 3.600.000.000
final int nanosecond; // 3.600.000.000.000
TimerWidget({
this.hours,
this.minutes,
#required this.seconds,
this.millisecond,
this.microsecond,
this.nanosecond,
});
#override
_TimerWidgetState createState() => _TimerWidgetState();
}
class _TimerWidgetState extends State<TimerWidget> {
Timer _timer;
var start = 30;
void startTimer() {
const oneSec = const Duration(seconds: 1);
_timer = new Timer.periodic(
oneSec,
(Timer timer) => setState(
() {
if (start < 1) {
timer.cancel();
} else {
start = start - 1;
}
},
),
);
}
#override
void dispose() {
_timer.cancel();
super.dispose();
}
Widget build(BuildContext context) {
return new Scaffold(
appBar: AppBar(title: Text("demo")),
body: Center(
child: Column(
children: <Widget>[
RaisedButton(
onPressed: () {
startTimer();
},
child: Text("start"),
),
Text("$start")
],
),
),
);
}
}
void main() {
runApp(MyApp());
}
class MyApp extends StatelessWidget {
#override
Widget build(BuildContext context) {
return MaterialApp(
title: 'Flutter Demo',
theme: ThemeData(
primarySwatch: Colors.blue,
visualDensity: VisualDensity.adaptivePlatformDensity,
),
home: TimerWidget(seconds: 30),
);
}
}
class MyHomePage extends StatefulWidget {
MyHomePage({Key key, this.title}) : super(key: key);
final String title;
#override
_MyHomePageState createState() => _MyHomePageState();
}
class _MyHomePageState extends State<MyHomePage> {
int _counter = 0;
void _incrementCounter() {
setState(() {
_counter++;
});
}
#override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text(widget.title),
),
body: Center(
child: Column(
mainAxisAlignment: MainAxisAlignment.center,
children: <Widget>[
Text(
'You have pushed the button this many times:',
),
Text(
'$_counter',
style: Theme.of(context).textTheme.headline4,
),
],
),
),
floatingActionButton: FloatingActionButton(
onPressed: _incrementCounter,
tooltip: 'Increment',
child: Icon(Icons.add),
),
);
}
}