how to send data through different classes in different screens in flutter - dart

Question

i was struck here while making an application my code went like this
void main() {
runApp(Myapp());
}
class Myapp extends StatelessWidget {
bool s=false;
#override
Widget build(BuildContext context) {
return (MaterialApp(
debugShowCheckedModeBanner: false,
title: "haha app",
theme: ThemeData(primarySwatch: Colors.lime),
home: s ? HomeScreen(null) : LoginPage()));
}
}
the above code is of main.dart file
and this is my another file called Login.dart and the code goes like this
class LoginPage extends StatefulWidget {
#override
_LoginPageState createState() => _LoginPageState();
}
class _LoginPageState extends State<LoginPage> {
Widget build(BuildContext context) {
return(some button ontap:(\\ on tap on this i have to change the bool s value in main.dart to true how to do that){
}
)
}
on tap the button the value s in main dart file should change to true but without navigator because we are not navigating here just a click.
please help me,
thanks in advance

Answer 1

You can use callbacks to communicate your widgets, like this
Create a method to get the callback , in this case : onChangeBool , pass the callback to your LoginPage Widget.
class Myapp extends StatelessWidget {
bool s=false;
onChangeBool(){
//change your var here
s = true;
//refresh the state
setState(() {
});
}
#override
Widget build(BuildContext context) {
return (MaterialApp(
debugShowCheckedModeBanner: false,
title: "haha app",
theme: ThemeData(primarySwatch: Colors.lime),
home: s ? HomeScreen(null) : LoginPage(onPressed: () => onChangeBool() ));
}
}
Receive the callBack , and call it when you press the button
class LoginPage extends StatefulWidget {
final VoidCallback onPressed;
LoginPage({this.onPressed});
#override
_LoginPageState createState() => _LoginPageState();
}
class _LoginPageState extends State<LoginPage> {
Widget build(BuildContext context) {
return RaisedButton(
child: Text("button"),
onPressed: (){
widget.onPressed();
},
)
}
)
}
In case you want to pass Data, you can use ValueChanged callback , or if you want to pass complex data, create your own callback using typedef/
A sample using ValueChanged.
class Myapp extends StatelessWidget {
bool s=false;
receiveData(String data){
print("your text here : $data");
}
#override
Widget build(BuildContext context) {
return (MaterialApp(
debugShowCheckedModeBanner: false,
title: "haha app",
theme: ThemeData(primarySwatch: Colors.lime),
home: s ? HomeScreen(null) : LoginPage(onPressed: receiveData ));
}
}
class LoginPage extends StatefulWidget {
final ValueChanged<String> onPressed;
LoginPage({this.onPressed});
#override
_LoginPageState createState() => _LoginPageState();
}
class _LoginPageState extends State<LoginPage> {
Widget build(BuildContext context) {
return RaisedButton(
child: Text("button"),
onPressed: (){
widget.onPressed("passing this data");
},
)
}
)
}