how pass variable from a class to another class in flutter - flutter

Question

I have the numOfItems set in this class and I want to use it in another class AddToCart, but I cant pass the variable successfully.. here is a sample code, please how can I do this, I cannot seem to figure it out, What I want to know is the best way to pass data after I have setState to the other class..
static int numOfItems = 1;
#override
Widget build(BuildContext context) {
return Row(
children: <Widget>[
buildOutlineButton(
icon: Icons.remove,
press: () {
if(numOfItems > 1){
setState(() {
numOfItems--;
});
}
},
),
Padding(
padding: const EdgeInsets.symmetric(horizontal: kDefaultPaddin / 2),
child: Text(
//"01",
numOfItems.toString().padLeft(2, "0"),
style: Theme.of(context).textTheme.headline,
),
),
buildOutlineButton(
icon: Icons.add,
press: () {
setState(() {
numOfItems++;
});
}),
],
);
}
SizedBox buildOutlineButton({IconData icon, Function press}) {
return SizedBox(
width: 32,
height: 32,
child: OutlineButton(
padding: EdgeInsets.zero,
shape: RoundedRectangleBorder(
borderRadius: BorderRadius.circular(10),
),
onPressed: press,
child: Icon(icon),
),
);
}
}```
here is the second class where I want to use the numOfItems in the second class, how can I access the variable in this class.
```class AddToCart extends StatelessWidget {
const AddToCart({
Key key,
}) : super(key: key);
#override
Widget build(BuildContext context) {
Size size = MediaQuery.of(context).size;
return Padding(
padding: const EdgeInsets.symmetric(vertical: kDefaultPaddin),
child: Row(
children: <Widget>[
Container(
margin: EdgeInsets.only(right:kDefaultPaddin),
height:50,
width: size.width * 0.3,
decoration: BoxDecoration(
border: Border.all(color:primaryColorDark),
borderRadius: BorderRadius.circular(18),
),
child: IconButton(
icon: SvgPicture.asset(
"assets/icons/add_to_cart.svg", color: primaryColorDark,), //svgPicture.asser
onPressed: () {
// on press of the cart button
},
),
),
Expanded(
child: SizedBox(
height:50,
child: FlatButton(
shape: RoundedRectangleBorder(
borderRadius: BorderRadius.circular(18)
),
color: primaryColor,
onPressed: (){
addProductToCart(context);
},
child: Text(
"Buy Now".toUpperCase(),
style: TextStyle(
fontSize: 17,
fontWeight: FontWeight.bold,
color: Colors.white,
)
),
),
),
)
],
),
);
}
void addProductToCart(BuildContext context) {
String quantityToSend = numOfItems
}
}
}```
What I want to know is the best way to pass data after I have setState to the other class..

Answer 1

You can use constructor to pass variable
Example:
Screen1:
class _TabsPageState extends State<TabsPage> {
int args = 3;
#override
Widget build(BuildContext context) {
return Scaffold(
body: Center(
child: FlatButton(
color: Colors.blueAccent,
child: Text('Navigate to home', style: TextStyle(color: Colors.white),),
onPressed: () {
print('123');
Navigator.pushReplacement(context, MaterialPageRoute(builder: (_) => Tab2Page(args)));
},
),
),
);
}
}
Screen2:
class Tab2Page extends StatelessWidget {
final int args;
Tab2Page(this.args);
#override
Widget build(BuildContext context) {
return Scaffold(
body: Center(
child: Text(args.toString()),
),
);
}
}

Answer 2

If you need only this variable " If it widget " just use the name of class x and then . then the name of static variable
i.e x.numOfItems
If this a another screen and you want to pass the data to this screen you can do it like this
class SecondScreen{
var anyVariable;
XScreen(this.anyVariable);
.......
......
}
onTap: () {
Navigator.push(
context,
MaterialPageRoute(
builder: (context) => SecondScreen(anyVariable :numOfItems),
),
);
},