disappearing_fab_navigator.dart

import 'dart:async';

import 'package:flutter/material.dart';

void main() => runApp(MyApp());

Stream<bool> get isFABVisible => _isFABVisibleController.stream;
final _isFABVisibleController = StreamController<bool>.broadcast();

class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

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

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

class _MyHomePageState extends State<MyHomePage> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: Text(widget.title)),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            RaisedButton(
              child: Text("Push new page"),
              onPressed: () {
                Navigator.push(
                  context,
                  MaterialPageRoute(builder: (context) => NewPage()),
                );
              },
            ),
          ],
        ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: () {},
        child: Icon(Icons.add),
      ),
    );
  }
}

class NewPage extends StatelessWidget {
  const NewPage({Key key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return StreamBuilder<bool>(
      stream: isFABVisible,
      initialData: true,
      builder: (context, snapshot) {
        return Scaffold(
          appBar: AppBar(title: Text('Next page')),
          body: Center(
            child: Column(
              mainAxisAlignment: MainAxisAlignment.center,
              children: <Widget>[
                RaisedButton(
                  onPressed: () => _isFABVisibleController.add(false),
                  child: Text("Press to make FAB disappear"),
                ),
                RaisedButton(
                  onPressed: () => _isFABVisibleController.add(true),
                  child: Text("Press to make FAB reappear"),
                ),
              ],
            ),
          ),
          floatingActionButton: snapshot.data
            ? FloatingActionButton(
              onPressed: () {},
              child: Icon(Icons.remove_circle),
            )
            : null,
        );
      },
    );
  }
}