CODEWITHSUNDEEP
flutterdart
juztcode
juztcode

Reputation: 1345

defining state in flutter

I was learning a bit of flutter, and I came across part where we define states, a class was given something like this:

class _sButtonState extends State<sButton>{
@override
Widget build(BuildContext context){
    return Container(
       RaisedButton(
            color: Colors.red,
            child: widget.child,
            onPressed: widget.onPressed,
        )
      );
  }
}

widget wasn't an instance nor class variable defined anywhere. So, I could only assume it was something implicitly provided by the dart framework. So, my question is:

  1. What is widget
  2. What is widget.child
  3. What is widget.onPressed
  4. and what are such implicitly provided variables in dart called?

Upvotes: 0

Views: 92

Answers (1)

Peter Haddad
Peter Haddad

Reputation: 80914

widget is a property in the State class, since _sButtonState extends State then your class inherits those properties and methods.

The current configuration.

A State object's configuration is the corresponding StatefulWidget instance. This property is initialized by the framework before calling initState. If the parent updates this location in the tree to a new widget with the same runtimeType and Widget.key as the current configuration, the framework will update this property to refer to the new widget and then call didUpdateWidget, passing the old configuration as an argument.

For example:

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);

  final String title;

  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  int _counter = 0;

  void _incrementCounter() {
    setState(() {
      _counter++;
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),

title property is an instance variable in the class MyHomePage which extends StatefulWidget and since State<T extends StatefulWidget>, then you can use the custom class MyHomePage and call widget.title

Upvotes: 1

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