How Can I PAUSE or RESUME a async task using a button in flutter? - flutter

Question

I'm Building An Flutter Application which requires image changes after a period of time. I thought using while loop with a sleep method inside may solve the problem. But It didn't, Image is only getting change after the loop ends. Application UI also gets froze.
So, I used the async Task which I can't control with a Button.
Desired Output: Image should be changed after every 10 seconds and the user can pause or resume method execution.
import 'package:flutter/material.dart';
void main() => runApp(MyApp());
class MyApp extends StatelessWidget {
// This widget is the root of your application.
#override
Widget build(BuildContext context) {
return MaterialApp(
home: Scaffold(
body: Center(
child: Test(
),
),
)
);
}}
class Test extends StatefulWidget {
#override
_TestState createState() => _TestState();
}
class _TestState extends State<Test> {
int imgnumber=1;
int varToCheckButtonPress = 0;
String BtnTxt = "START";
void inc(){
while(imgnumber<10)
{
print(imgnumber);
await Future.delayed(const Duration(seconds: 10));
setState(() {
imgnumber++;
});
}
}
#override
Widget build(BuildContext context) {
return Column(
crossAxisAlignment: CrossAxisAlignment.stretch,
children: <Widget>[
Expanded(flex: 1,
child: Container(
child: Image.asset('images/'+imgnumber.toString()+'.png'),
height: 500,
width:500,
color: Colors.green,
),
),
FlatButton(
child: Text(BtnTxt),
onPressed: (){
if (varToCheckButtonPress == 0) {
setState(() {
inc();
BtnTxt = 'PAUSE';
varToCheckButtonPress = 1;
});
} else if (varToCheckButtonPress == 1) {
setState(() {
BtnTxt = 'RESUME';
varToCheckButtonPress = 0;
});
}
},
)
],
);
}
}
I want the user to control the UI with a single button behave as START, PAUSE and RESUME.
Can we Use normal function To implement this functionality?

Answer 1

You should make use of Bloc pattern to manage your states, e.g: StreamBuilder, Providers, and make a timer to push new imageUrl to the sink and let the streamBuilder receive the latest imageUrl.
As for your button, all it controls is the timer. When u hit the play button, new imageUrl will keep pushing to the sink, while you press paused, simply stop the timer, and new image Url will not be pushing new imageUrl to the sink, and of course, reset the timer when you hit the stop button.
Here is a very detail Bloc pattern tutorial you can follow: Medium

Answer 2

The shortcut to achieve this is :
You can probably hold a function in async loop and call setState method on tap to change it's state.
For example :
call this function in desired location
while (_isPaused) {
await Future.delayed(Duration(milliseconds: 500));
}
and then call set state method from onTap, just like this
onTap:(){
setState((){
_isPaused? _isPaused=false: _isPaused=true;
});
}