StatefulBuilder Widget in Flutter

Sanjeev

28 April 2023

In this article, we are going to learn about the StatefulBuilder widget in flutter and will also learn when and where to use this widget.

StatefulBuilder is a widget having a mutable state (whose state can be changed). What makes it’s special is that it only rebuilds the particular widget that is wrapped under the Stateful Builder.

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This widget provides a state setter method that is responsible for the rebuilding of the widget.

KEEP IN MIND

The widgets that you want to update should be kept inside this widget.

For example:

The Below code will not work, i.e the text in the Text widget will not update because it needs to be wrapped in this widget.

int count = 0;

@override
Widget build(BuildContext context) {
...
    Column(
          children: &lt;Widget&gt;&#91;
            StatefulBuilder(builder: (context, setState) {
              return ElevatedButton(
                  onPressed: () {
                    setState(() {
                      count++;
                    });
                  },
                  child: Text("Add"));
            }),
            Text("$count")
          ],
        ),
...
}

int count = 0;

@override

Widget build(BuildContext context) {

...

Column(

children: <Widget>[

StatefulBuilder(builder: (context, setState) {

return ElevatedButton(

onPressed: () {

setState(() {

count++;

});

child: Text("Add"));

}),

Text("$count")

...

}

What you need to do here is this:

int count = 0;

@override
Widget build(BuildContext context) {
...
    StatefulBuilder(builder: (context, setState) {
          return Column(
            children: &lt;Widget&gt;&#91;
              ElevatedButton(
                onPressed: () {
                  setState(() {
                    count++;
                  });
                },
                child: Text("Add"),
              ),
              Text("$count")
            ],
          );
        })
...
}

int count = 0;

@override

Widget build(BuildContext context) {

...

StatefulBuilder(builder: (context, setState) {

return Column(

children: <Widget>[

ElevatedButton(

onPressed: () {

setState(() {

count++;

});

child: Text("Add"),

Text("$count")

);

})

...

}

Now the above code will work perfectly.

Can we replace stateful widget with statefulbuilder widget?

We cannot replace the stateful widget with this widget because Flutter only preserves associated states that we provide in stateful widgets.

...
@override
State&lt;HomePage&gt; createState() =&gt; _HomePageState();
...

class _HomePageState extends State&lt;HomePage&gt; {
...

...

@override

State<HomePage> createState() => _HomePageState();

...

class _HomePageState extends State<HomePage> {

...

If we use a stateful builder widget and store any state in instance variables in the stateless widget it may be lost at any time as the constructor for the stateless widget may be called multiple times, just like the build method.

Conclusion

Now we know how to use the stateful builder widget in flutter. We also know why we cannot replace the stateful widget with this widget.

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Reference: Can Stateful Builder Step into the shoes of Stateful Widget?