CODEWITHSUNDEEP
mobiledartflutter
Durdu
Durdu

Reputation: 4849

BuildContex + widget tree

I am following flutter's documentation about the BuildContext class because it is not clear for me how and why to use this class.

  Widget build(BuildContext context) {
    // here, Scaffold.of(context) returns null
    return Scaffold(
      appBar: AppBar(title: Text('Demo')),
      body: Builder(
        builder: (BuildContext context) {
          return FlatButton(
            child: Text('BUTTON'),
            onPressed: () {
              // here, Scaffold.of(context) returns the locally created Scaffold
              Scaffold.of(context).showSnackBar(SnackBar(
                content: Text('Hello.')
              ));
            }
          );
        }
      )
    );
  }

I do not get this paragraph:

The BuildContext for a particular widget can change location over time as the widget is moved around the tree. Because of this, values returned from the methods on this class should not be cached beyond the execution of a single synchronous function.

BuildContext objects are actually Element objects. The BuildContext interface is used to discourage direct manipulation of Element objects.

as the widget is moved around the tree -> how does this happen?

As per my understanding (and please correct me if I am wrong here) the widget tree is basically how the widgets are "stacked" and how they build each other. Since it is not recommended to have sub-widgets referenced as properties in your CustomWidget class how do I change the position in a tree of a widget returned during the build method (or how does this happen by default because of the framework)

Upvotes: 0

Views: 314

Answers (1)

Rémi Rousselet
Rémi Rousselet

Reputation: 277487

This tree change typically happens when the build method conditionally build its descendants

Example:

Widget build(BuildContext context) {
  return condition
    ? Foo()
    : Bar(child: Foo());
}

With such build method, the BuildContext of the Foo widget changes when condition changes.

Upvotes: 1

Related Questions