How to change title of main.dart AppBar in it's child programmatically?

Have a BLoC for app properties in app_properties_bloc.dart

final appBloc = AppPropertiesBloc(); class AppPropertiesBloc{ StreamController<String> _title = StreamController<String>(); Stream<String> get titleStream => _title.stream; updateTitle(String newTitle){ _title.sink.add(newTitle); } dispose() { _title.close(); } } 

Use stream builder in AppBar like this:

AppBar( title: StreamBuilder<Object>( stream: appBloc.titleStream, initialData: "Main Dart", builder: (context, snapshot) { return Text(snapshot.data); } ), ), 

Use this to update title on button's onPressed()

onPressed: () { appBloc.updateTitle('new title'); }, 

Just in case you are changing only the title of Scaffold then this will work.

I am creating a DefaultScaffold with the title each screen provides. Here the code will show the MainPage and two other pages which have the same AppBar with changed titles.

void main() { runApp(MyApp()); } class MyApp extends StatelessWidget { @override Widget build(BuildContext context) { return MaterialApp(initialRoute: 'home', routes: <String, WidgetBuilder>{ 'home': (context) => SOMain(), '/secondPage': (context) => DefaultScaffold("Second Screen", SOSecond()), '/thirdPage': (context) => DefaultScaffold("Third Screen", SOThird()), }); } } class DefaultScaffold extends StatelessWidget { String title; Widget body; DefaultScaffold(this.title, this.body); @override Widget build(BuildContext context) { return Scaffold( appBar: AppBar( title: Text(title), ), body: body, ); } } class SOMain extends StatelessWidget { @override Widget build(BuildContext context) { return DefaultScaffold( "Main Screen", Center( child: RaisedButton( child: Text("Go to second screen"), onPressed: () { Navigator.pushNamed(context, '/secondPage'); }), ), ); } } class SOSecond extends StatelessWidget { @override Widget build(BuildContext context) { return Center( child: RaisedButton( child: Text("Go the 3rd screen"), onPressed: () => Navigator.pushNamed(context, "/thirdPage"), ), ); } } class SOThird extends StatelessWidget { @override Widget build(BuildContext context) { return Center(child: Text("You are on last screen")); } } 

Note: This is a simple workaround and may not be the best way to do this.

You can accomplish updating the state of the parent from a child by using a callback function.

Parent Class:

import 'package:flutter/material.dart'; class Parent extends StatefulWidget { @override State<StatefulWidget> createState() { return ParentState(); } } class ParentState extends State<Parent> { String title = "Old Title"; @override Widget build(BuildContext context) { return new Scaffold( appBar: new AppBar( title: new Text(title), ), body: DaysFragmentView(onTitleSelect: (String value) { setTitle(value); } ), ); } void setTitle(String value) { setState(() { title = value; }); } } 

Child Class

 typedef TitleCallback = void Function(Title color); class DaysFragmentView extends StatelessWidget { const DaysFragmentView({this.onTitleSelect}); final TitleCallback onTitleSelect; @override Widget build(BuildContext context) { return Row( children: <Widget>[ RaisedButton( child: Text('One'), onPressed: () { onTitleSelect("TITLE ONE"); }, ), RaisedButton( child: Text('Two'), onPressed: () { onTitleSelect("TITLE TWO"); }, ) ], ); } } 

Reference:

• call-method-in-one-stateful-widget-from-another-stateful-widget-flutter

• working-with-callback-in-flutter

Using ValueListenableBuilder is an option.

Use an instance variable

String appTitle; 

Then set the app bar as in the following block:

appBar: AppBar( ValueListenableBuilder<String>( valueListenable: appTitle, builder: (context, value, child) { return Text(appTitle.value); }, ), 

After that you can simply set appTitle.value in the other class. The title will be changed too because it listens to that value.

appTitle.value = "Home Screen"; 

Some answer here are too complicated. Here is a full working example using app bar update from child with scafold widget.

You can run the example in dart pad

import 'package:flutter/material.dart'; void main() { runApp(const MyHomePage(title: 'init title')); } class MyHomePage extends StatefulWidget { const MyHomePage({super.key, required this.title}); final String title; @override State<MyHomePage> createState() => _MyHomePageState(); } class _MyHomePageState extends State<MyHomePage> { final ValueNotifier<String?> _appBarTitleNotifier = ValueNotifier<String?>(null); @override Widget build(BuildContext context) { return MaterialApp( home: Scaffold( appBar: AppBar( title: ValueListenableBuilder<String?>( builder: (BuildContext context, String? value, Widget? child) { return Text(value ?? widget.title); }, valueListenable: _appBarTitleNotifier, ), ), body: Center( child: Column( mainAxisAlignment: MainAxisAlignment.center, children: <Widget>[ ChildDemoTitleBar(titleNotifier: _appBarTitleNotifier) ], ), ), ), ); } } class ChildDemoTitleBar extends StatefulWidget { final ValueNotifier<String?> titleNotifier; const ChildDemoTitleBar({Key? key, required this.titleNotifier}) : super(key: key); @override State<ChildDemoTitleBar> createState() => _ChildDemoTitleBarState(); } class _ChildDemoTitleBarState extends State<ChildDemoTitleBar> { int _counter = 0; @override Widget build(BuildContext context) { return Padding( padding: const EdgeInsets.fromLTRB(20, 0, 20, 20), child: InkWell( onTap: () { _counter++; widget.titleNotifier.value = "title updated $_counter"; }, child: const Text("tap to update title"))); } }