CODEWITHSUNDEEP
flutternavigatorstatefulwidget
wurikiji
wurikiji

Reputation: 327

What are the internal implementations of Navigator.push() and Navigator.pop()?

In a State class, despite not calling setState() call, it is rebuilt with new items when the widget is returned from Navigator.pop(). How could this happen?

On my simplified code below, the ListView is rebuilt whenever I clicked a button and pop the pushed widget.

Is it because Navigator.push() disposes a current widget and the widget is re-rendered after Navigator.pop() ? 

class _TestState extends State<Test> {
  List<int> initialList = [];
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      floatingActionButton: FlatButton(
        onPressed: () async {
          var nothing = await Navigator.of(context).push(
            MaterialPageRoute(builder: (_context) => PushedWidget()),
          );
          // the State is rebuilt without calling setState()
          initialList.add(1);
        },
        child: Text('test'),
      ),
      body: Container(
        child: ListView.builder(
          itemCount: initialList.length,
          itemBuilder: (context, idx) {
            return Text('${initialList[idx]}');
          },
        ),
      ),
    );
  }
}

class PushedWidget extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(leading: IconButton(onPressed: () => _pop(context), icon: Icon(Icons.close))),
    );
  }
  void _pop(BuildContext context) {
    Navigator.of(context).pop('popped');
  }
}

I've read docs and codes of implementation. But I couldn't find the answer to this question.

Upvotes: 0

Views: 153

Answers (1)

Hussam
Hussam

Reputation: 1706

Navigator maintains a stack-based history of child widgets. I am considering that you already know about the data structure Stack. Navigator.push and Navigator.push works same like Stack. When we navigate to another screen, we use the push methods and Navigator widget adds the new screen onto the top of the stack. Whereas, the pop methods would remove that screen from the stack.

Upvotes: 1

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