Flutter - Create a countdown widget - dart

Question

I am trying to build a countdown widget. Currently, I got the structure to work. I only struggle with the countdown itself. I tried this approach using the countdown plugin:
class _Countdown extends State<Countdown> {
int val = 3;
void countdown(){
CountDown cd = new CountDown(new Duration(seconds: 4));
cd.stream.listen((Duration d) {
setState((){
val = d.inSeconds;
});
});
}
#override
build(BuildContext context){
countdown();
return new Scaffold(
body: new Container(
child: new Center(
child: new Text(val.toString(), style: new TextStyle(fontSize: 150.0)),
),
),
);
}
}
However, the value changes very weirdly and not smooth at all. It start twitching. Any other approach or fixes?

Answer 1

It sounds like you are trying to show an animated text widget that changes over time. I would use an AnimatedWidget with a StepTween to ensure that the countdown only shows integer values.
import 'package:flutter/material.dart';
void main() {
runApp(new MaterialApp(
home: new MyApp(),
));
}
class Countdown extends AnimatedWidget {
Countdown({ Key key, this.animation }) : super(key: key, listenable: animation);
Animation<int> animation;
#override
build(BuildContext context){
return new Text(
animation.value.toString(),
style: new TextStyle(fontSize: 150.0),
);
}
}
class MyApp extends StatefulWidget {
State createState() => new _MyAppState();
}
class _MyAppState extends State<MyApp> with TickerProviderStateMixin {
AnimationController _controller;
static const int kStartValue = 4;
#override
void initState() {
super.initState();
_controller = new AnimationController(
vsync: this,
duration: new Duration(seconds: kStartValue),
);
}
#override
Widget build(BuildContext context) {
return new Scaffold(
floatingActionButton: new FloatingActionButton(
child: new Icon(Icons.play_arrow),
onPressed: () => _controller.forward(from: 0.0),
),
body: new Container(
child: new Center(
child: new Countdown(
animation: new StepTween(
begin: kStartValue,
end: 0,
).animate(_controller),
),
),
),
);
}
}

Answer 2

The countdown() method should be called from the initState() method of the State object.
class _CountdownState extends State<CountdownWidget> {
int val = 3;
CountDown cd;
#override
void initState() {
super.initState();
countdown();
}
...
Description of initState() from the Flutter docs:
The framework calls initState. Subclasses of State should override
initState to perform one-time initialization that depends on the
BuildContext or the widget, which are available as the context and
widget properties, respectively, when the initState method is called.
Here is a full working example:
import 'dart:async';
import 'package:flutter/material.dart';
import 'package:countdown/countdown.dart';
void main() {
runApp(new MyApp());
}
class MyApp extends StatelessWidget {
#override
Widget build(BuildContext context) {
return new MaterialApp(
title: 'Countdown Demo',
theme: new ThemeData(
primarySwatch: Colors.blue,
),
home: new MyHomePage(),
);
}
}
class MyHomePage extends StatelessWidget {
#override
Widget build(BuildContext context) {
return new CountdownWidget();
}
}
class _CountdownState extends State<CountdownWidget> {
int val = 3;
CountDown cd;
#override
void initState() {
super.initState();
countdown();
}
void countdown(){
print("countdown() called");
cd = new CountDown(new Duration(seconds: 4));
StreamSubscription sub = cd.stream.listen(null);
sub.onDone(() {
print("Done");
});
sub.onData((Duration d) {
if (val == d.inSeconds) return;
print("onData: d.inSeconds=${d.inSeconds}");
setState((){
val = d.inSeconds;
});
});
}
#override
build(BuildContext context){
return new Scaffold(
body: new Container(
child: new Center(
child: new Text(val.toString(), style: new TextStyle(fontSize: 150.0)),
),
),
);
}
}
class CountdownWidget extends StatefulWidget {
#override
_CountdownState createState() => new _CountdownState();
}

Answer 3

based on #raju-bitter answer, alternative to use async/await on countdown stream
void countdown() async {
cd = new CountDown(new Duration(seconds:4));
await for (var v in cd.stream) {
setState(() => val = v.inSeconds);
}
}

Answer 4

Why not use a simple TweenAnimationBuilder its easy to use and you don't need to manage any stream controllers or worry about using streams and disposing them off etc;
TweenAnimationBuilder<double>(
duration: Duration(seconds: 10),
tween: Tween(begin: 100.0, end: 0.0),
onEnd: () {
print('Countdown ended');
},
builder: (BuildContext context, double value, Widget child) {
return Padding(
padding: const EdgeInsets.symmetric(vertical: 5),
child: Text('${value.toInt()}',
textAlign: TextAlign.center,
style: TextStyle(
color: Colors.black,
fontWeight: FontWeight.bold,
fontSize: 40)));
}),
here's the dartpad example to playaround
output:
originally answered here

Answer 5

Countdown example using stream, not using setState(...) therefore its all stateless.
this borrow idea from example flutter_stream_friends
import 'dart:async';
import 'package:flutter/material.dart';
import 'package:countdown/countdown.dart';
void main() {
runApp(new MyApp());
}
class MyApp extends StatelessWidget {
static String appTitle = "Count down";
#override
Widget build(BuildContext context) {
return new MaterialApp(
title: appTitle,
theme: new ThemeData(
primarySwatch: Colors.purple,
),
home: new StreamBuilder(
stream: new CounterScreenStream(5),
builder: (context, snapshot) => buildHome(
context,
snapshot.hasData
// If our stream has delivered data, build our Widget properly
? snapshot.data
// If not, we pass through a dummy model to kick things off
: new Duration(seconds: 5),
appTitle)),
);
}
// The latest value of the CounterScreenModel from the CounterScreenStream is
// passed into the this version of the build function!
Widget buildHome(BuildContext context, Duration duration, String title) {
return new Scaffold(
appBar: new AppBar(
title: new Text(title),
),
body: new Center(
child: new Text(
'Count down ${ duration.inSeconds }',
),
),
);
}
}
class CounterScreenStream extends Stream<Duration> {
final Stream<Duration> _stream;
CounterScreenStream(int initialValue)
: this._stream = createStream(initialValue);
#override
StreamSubscription<Duration> listen(
void onData(Duration event),
{Function onError,
void onDone(),
bool cancelOnError}) =>
_stream.listen(onData,
onError: onError, onDone: onDone, cancelOnError: cancelOnError);
// The method we use to create the stream that will continually deliver data
// to the `buildHome` method.
static Stream<Duration> createStream(int initialValue) {
var cd = new CountDown(new Duration(seconds: initialValue));
return cd.stream;
}
}
The difference from stateful is that reload the app will restart counting. When using stateful, in some cases, it may not restart when reload.