Difference Consumer / Provider.of in ChangeNotifierProvider - flutter

Question

I don't really understand the difference between Provider.of() and Consumer.
I have read here that Consumer is like Provider.of with listen: true.
However, in the bellow example, I don't get an error when I use Consumer, but I get one while using Provider.of. I am forced to use listen: false. The below example is the default flutter app with ChangeNotifierProvider implemented.
I will just change the code in floatingActionButton in main.dart to see diffences between Consumer, Provider.of listen: true and Provider.of listen: false
Code of counter.dart
import 'package:flutter/material.dart';
class Counter extends ChangeNotifier {
int value = 0;
void increment() {
value++;
notifyListeners();
}
void decrement() {
value--;
notifyListeners();
}
}
Full code of main.dart, with floatingActionButton using Consumer. It is working
import 'package:flutter/material.dart';
import 'package:provider/provider.dart';
import 'package:unit_test/counter.dart';
void main() {
runApp(MyApp());
}
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,
visualDensity: VisualDensity.adaptivePlatformDensity,
),
home: ChangeNotifierProvider<Counter>(
create: (context) => Counter(),
child: 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>[
Text(
'You have pushed the button this many times:',
),
Consumer<Counter>(builder: (context, counter, child) {
return Text(
counter.value.toString(),
style: Theme.of(context).textTheme.headline4,
);
}),
],
),
),
floatingActionButton:
Consumer<Counter>(builder: (context, counter, child) {
return FloatingActionButton(
onPressed: () {
counter.increment();
},
tooltip: 'Increment',
child: Icon(Icons.add),
);
}),
);
}
}
Code of floatingActionButton using Provider.of, listen: true, not working
floatingActionButton: FloatingActionButton(
onPressed: () {
Provider.of<Counter>(context, listen: true).increment();
},
tooltip: 'Increment',
child: Icon(Icons.add),
),
Error : Tried to listen to a value exposed with provider, from outside of the widget tree...
Code of floatingActionButton using Provider.of, listen: false, working
floatingActionButton: FloatingActionButton(
onPressed: () {
Provider.of<Counter>(context, listen: false).increment();
},
tooltip: 'Increment',
child: Icon(Icons.add),
),
I don't get it. I put listen: false, but it is still listening and rebuilding the widget
Thank you for your help

Answer 1

listen:true needs to put inside a build widget tree. It purpose is to rebuild the whole widget if called (notifyListener).
#override
Widget build(BuildContext context) {
Counter counter = Provider.of<Counter>(context, listen: true);
...
counter.increment(); // Will rebuild entire widget.
...
Consumer is a widget that call listen:true inside it but will only rebuild it's child widget.
Consumer<Counter>(builder: (_, counter, __) {
return Column(
children:[
TextButton(
onPressed: () => counter.increment(), // Will only rebuild this Column
child: Icon(Icons.add),),
Text(counter.value.toString());
}),
listen:false will access Provider without rebuild widget if called.
TextButton(
onPressed: () {
Counter counter = Provider.of<Counter>(context, listen: false);
counter.increment();
// Will change Provider value, but won't rebuild. It will make widget that has
// Consumer as parent to rebuild (or with listen:true to rebuild).
}
child: Icon(Icons.add),
),