Multiple questions related to Flutter basic

Question

I am coming from React and trying to understand Flutter. There are some differences between dart vs JS and React vs Flutter. However, it seems a bit similar to each other. However, there is some confusion toward Flutter.

void

It does not return the value. Therefore, it is used to void main(). Does it mean like the function 'main()' will be executed and I will never be able to reuse void main()?

<>

In the code, I have here

class LoginScreen extends StatefulWidget {
  createState() {
    return new LoginScreenState();
  }
}

class LoginScreenState extends State<LoginScreen> {
  Widget build(context) {
    return Container(
        margin: EdgeInsets.all(20.0),
        child: Column(
          children: [
            emailField(),
            // passwordField(),
            // submitButton(),
          ],
        ));
  }
}

I can see that State<LoginScreen> is related to class LoginScreen. It is an extension of the LoginScreen State?

Future<int> successor = future.then((int value) {
  
  },

However, in here Future <----- I do not understand why it has to state 'int' in this code. What is the proper use of <>?

Stateful vs Stateless

Can I just use the Stateful all the time even if I do not have any state like React? Where there is no difference?

That main() returns void has nothing to do with it being reusable or not. It's called for its side-effect, just like other functions that returnvoid (e.g. print). Normally you wouldn't want or need to call main() again, though. — jamesdlin
– jamesdlin, Commented Oct 28, 2020 at 18:47

Doc · Accepted Answer · 2020-10-28 19:36:30Z

2

You need to learn basic dart.

void main() is same as main(). The only difference is declaring the return type. main() is called only once by the flutter engine.
Read about generics. <> is the called the diamond operator and is used to specify the type of something. Future<int> means the function will return something in future and it will strictly be of int type. If you don't specify the type flutter will treat it as dynamic.
You can use stateful classes if you are using state management packages like provider or rxdart to maintain state.

edited Oct 28, 2020 at 19:36

answered Oct 28, 2020 at 12:47

Doc

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2 Comments

chichi Over a year ago

It is more close to TypeScript, as I see. I am also studying Dart as well. Thank you for the answers!

jamesdlin Over a year ago

main() is called automatically once, but it's still a function; it can be called multiple times like any other function. For example, main() could be recursive.

Sunil gohil · Accepted Answer · 2021-04-21 10:11:44Z

1

class LoginScreen extends StatefulWidget {
  createState() {
    return new LoginScreenState();
  }
}

    enter code here

changed to 
class LoginScreen extends StatefulWidget {
  LoginScreenState createState()=>LoginScreenState();
  }
}

    enter code here

Stateful vs Stateless`enter code here`
stateful has state object and stateless has no state object.using stateful you can changes widget data .on other hand in stateful you cant

answered Apr 21, 2021 at 10:11

Sunil gohil

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