Develop Reference

Exception when trying to use navigator

I am getting an exception: FlutterError (Navigator operation requested with a context that does not include a Navigator. The context used to push or pop routes from the Navigator must be that of a widget that is a descendant of a Navigator widget.)
This is the important code of the first page (Skipped some code with ... that wasn't relevant):
import 'package:google_fonts/google_fonts.dart';
import 'register.dart';
void main() async {
...
runApp(const MyApp());
}
class MyApp extends StatefulWidget {
const MyApp({Key? key}) : super(key: key);
#override
State<MyApp> createState() => _MyAppState();
}
class _MyAppState extends State<MyApp> {
...
#override
Widget build(BuildContext context) {
return MaterialApp(
debugShowCheckedModeBanner: false,
theme: ThemeData(
textTheme: GoogleFonts.interTextTheme(
Theme.of(context).textTheme,
)),
home: Scaffold(
body: Container(
width: double.infinity,
...
Align(
alignment: Alignment.centerRight,
child: TextButton(
onPressed: () {
Navigator.push(
context,
MaterialPageRoute(
builder: (context) => SecondRoute()));
},
child: Text(
"Forgot Password?",
style: GoogleFonts.inter(
fontWeight: FontWeight.w600,
),
),
),
),
...
),
));
}
}
This is the second page:
import 'package:flutter/material.dart';
class SecondRoute extends Navigator {
#override
Widget build(BuildContext context) {
return new Scaffold(
appBar: AppBar(
title: Text("Second Route"),
),
);
}
}
There are no syntax errors only exceptions thrown when the code is run. I have tried already looking for the solution but the other way of putting the material app in the runApp() method, to my understanding doesn't work for the way I use the Text Theme and use context.
Let me know if I need to give more code or context.
Any help would be greatly appreciated!

Try changing:
class SecondRoute extends Navigator {
#override
Widget build(BuildContext context) {
return new Scaffold(
appBar: AppBar(
title: Text("Second Route"),
),
);
}
}
to:
class SecondRoute extends StatelessWidget {
#override
Widget build(BuildContext context) {
return new Scaffold(
appBar: AppBar(
title: Text("Second Route"),
),
);
}
}
Edit, also move the scaffold from _MyAppState into it's own widget.
class FirstRoute extends StatelessWidget {
#override
Widget build(BuildContext context) {
return Scaffold(
body: SizedBox(
width: double.infinity,
child: Align(
alignment: Alignment.centerRight,
child: TextButton(
onPressed: () {
print('hello');
Navigator.push(
context,
MaterialPageRoute(builder: (context) => SecondRoute()),
);
},
child: Text(
"Forgot Password?",
style: GoogleFonts.inter(
fontWeight: FontWeight.w600,
),
),
),
),
),
);
}
}
And then use in _MyAppState like so:
class _MyAppState extends State<MyApp> {
#override
Widget build(BuildContext context) {
return MaterialApp(
theme: ThemeData(
textTheme: GoogleFonts.interTextTheme(
Theme.of(context).textTheme,
)),
home: FirstRoute(),
);
}
}

Is there a way to hide a container/elements after click on button in flutter?

As the title suggest I want to hide a container when button is clicked.

Try with this visibility
import 'package:flutter/material.dart';
import 'package:webview_flutter/webview_flutter.dart';
void main() {
runApp(MyApp());
}
class MyApp extends StatefulWidget {
// This widget is the root of your application.
#override
_MyAppState createState() => _MyAppState();
}
class _MyAppState extends State<MyApp> {
bool visible = true;
#override
Widget build(BuildContext context) {
return MaterialApp(
title: 'Flutter Demo',
home: Scaffold(
appBar: AppBar(
title: Text("Test obviously"),
),
body: Column(
crossAxisAlignment: CrossAxisAlignment.start,
children: [
TextButton(
onPressed: () {
setState(() {
visible = !visible;
});
},
child: Text("Click")),
Visibility(
visible: visible,
child: Container(
height: 100,
color: Colors.green,
))
],
),
));
}
}

bool isButtonClicked = false
ElevatedButton(
style: ElevatedButton.styleFrom(primary: Colors.amber),
onPressed: () => {
setState(() {
isButtonClicked = !isButtonClicked;
});
},
child: Text('Hide/Unhide Container'),
),
!isButtonClicked? Container(): Offstage();

Flutter: ListView disposes widgets when keyboard pops up

I have an app with a page that has a ListView.builder().
Each row of the list is a stateful widget (match_chat_row.dart).
When you click on that stateful widget, it's navigating to another stateful widget (chat_screen.dart).
chat_screen.dart has a TextField.
The problem is that last few widgets(match_chat_row.dart) of the ListView are being disposed when the keyboard pops up on one of the first match_chat_row's chat_screen.dart.
I made this simple app to demonstrate it:
main.dart
import 'package:flutter/material.dart';
import 'match_chat_row.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,
),
home: MyHomePage(title: 'Flutter Demo Home Page'),
);
}
}
class MyHomePage extends StatefulWidget {
MyHomePage({Key? key, required this.title}) : super(key: key);
final String title;
#override
_MyHomePageState createState() => _MyHomePageState();
}
class _MyHomePageState extends State<MyHomePage> {
final String _pageName = "Screen";
List<String> _chats = ["A","B","C","D","E","F","G","H","I","J"];
#override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text(widget.title),
),
body: _body()
);
}
_body(){
return ListView.builder(
itemCount: _chats.length,
itemBuilder: (_, index) => _buildRow(_chats[index]),
);
}
Widget _buildRow(String chat) {
return
Column(
key: ValueKey<String>('chat-$chat'),
children: [
Center(
child:
MatchChatRow(
content: chat,
),
),
Divider(color: Colors.grey.withOpacity(0.20), thickness: 0.8, height: 0.0,)
],
);
}
}
match_chat_row.dart
import 'package:flutter/material.dart';
import 'chat_screen.dart';
class MatchChatRow extends StatefulWidget {
final String content;
const MatchChatRow({required this.content});
#override
_MatchChatRowState createState() => _MatchChatRowState();
}
class _MatchChatRowState extends State<MatchChatRow> {
#override
void dispose(){
print("Disposed ROW! ${widget.content}");
super.dispose();
}
#override
Widget build(BuildContext context) {
final rowHeight = 100.0;
final rowPadding = 10.0;
return
InkWell(
onTap: () =>
Navigator.push(
context,
MaterialPageRoute(
builder: (context) => ChatScreen(
key: ValueKey(widget.content),
),
),
),
child:
Container(
height: rowHeight,
padding: EdgeInsets.all(rowPadding),
child: Row(
children: <Widget>[
SizedBox(
width: 20.0,
),
Expanded(
child:
Column(
mainAxisAlignment: MainAxisAlignment.center,
crossAxisAlignment: CrossAxisAlignment.start,
children: <Widget>[
Text(widget.content),
Text("_buildSubtitle()"),
],
)
),
],
),
)
);
}
}
chat_screen.dart
import 'dart:async';
import 'package:flutter/material.dart';
import 'package:flutter/services.dart';
class ChatScreen extends StatefulWidget {
const ChatScreen({required Key key,}): super(key: key);
#override
_ChatScreenState createState() => _ChatScreenState();
}
class _ChatScreenState extends State<ChatScreen> with TickerProviderStateMixin {
final TextEditingController _messageController = TextEditingController();
bool _isComposingMessage = false;
bool _isChatExist = false;
bool _isLoading = false;
bool _isSending = false;
#override
void initState() {
super.initState();
}
#override
void dispose(){
print("disposed chat! ${widget.key}");
super.dispose();
}
Container _buildMessageTF() {
return Container(
margin: const EdgeInsets.only(left: 8, right: 8, bottom: 8),
decoration: BoxDecoration(
border:
Border.all(color: Theme.of(context).accentColor.withOpacity(0.3)),
borderRadius: BorderRadius.circular(30)),
child: Row(
children: <Widget>[
Expanded(
child:
TextField(
minLines: 1,
maxLines: 4,
controller: _messageController,
textCapitalization: TextCapitalization.sentences,
onChanged: (messageText) {
setState(() => _isComposingMessage = messageText.isNotEmpty);
},
decoration: InputDecoration(
focusedBorder: InputBorder.none,
enabledBorder: InputBorder.none,
hintText: 'Message...'),
),
),
],
),
);
}
#override
Widget build(BuildContext context) {
return
WillPopScope(
onWillPop: () {
return Future.value(true);
},
child:
SafeArea(
child: Scaffold(
appBar: AppBar(
title: Text("Hi")
),
body:
SafeArea(
child: Column(
mainAxisAlignment: MainAxisAlignment.spaceBetween,
crossAxisAlignment: CrossAxisAlignment.stretch,
children: <Widget>[
if (!_isChatExist && !_isLoading) SizedBox.shrink(),
_buildMessageTF(),
],
),
),
),
)
);
}
}
And whenever I click on the TextField and the Keyboard pops up the below widgets are being disposed (this is my debug console):
I/flutter (23372): Disposed ROW! I
I/flutter (23372): Disposed ROW! J
I/flutter (23372): Disposed ROW! H

update your _body from main
_body(){
return SingleChildScrollView(
child: ListView.builder(
shrinkWrap: true,
physics: ScrollPhysics(),
itemCount: _chats.length,
itemBuilder: (_, index) => _buildRow(_chats[index]),
),
);
}

Persisting data in a flutter application

I am building an app and in it, I have the names of people in a list from which I could add/delete, etc.. The problem is this list is not saved when I close the app, which is inconvenient.
I heard you can use shared Preferences to save simple objects like this, without complicating things like using SQLite and json.
So I'd like to know what's the suggested way to persist this data and load it etc.
Thanks in Advance and have a great day :)
Here is the code:
import 'package:flutter/material.dart';
import 'package:zakif_yomi3/NewPerson.dart';
import 'package:shared_preferences/shared_preferences.dart';
void main() => runApp(MyApp());
class MyApp extends StatelessWidget {
#override
Widget build(BuildContext context) {
return MaterialApp(
title: 'Flutter Demo',
theme: ThemeData(
primarySwatch: Colors.purple,
),
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> {
final List<String> people = [];
void _addNewPerson(String name) {
setState(() {
people.add(name);
});
}
void _startAddNewPerson(BuildContext ctx) {
showModalBottomSheet(
context: ctx,
builder: (_) {
return GestureDetector(
onTap: () {},
child: NewPerson(_addNewPerson),
behavior: HitTestBehavior.opaque,
);
},
);
}
void _deletePerson(int value ) {
setState(() {
people.removeAt(value);
});
}
#override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
centerTitle: true,
title: Text(
'People',
style: TextStyle(fontSize: 30),
),
actions: <Widget>[
IconButton(
icon: Icon(Icons.add),
onPressed: () => _startAddNewPerson(context),
)
],
),
body: ListView.builder(
itemCount: this.people.length,
itemBuilder: (context, value) {
return Card(
color: Colors.amberAccent[200],
elevation: 3,
child: Container(
child: ListTile(
leading: Text(value.toString()),
title: Text(
people[value],
),
trailing: IconButton(
icon: Icon(Icons.delete),
onPressed: () {
_deletePerson(value);
},
),
),
),
);
},
),
);
}
}
And the NewPerson object:
import 'package:flutter/material.dart';
class NewPerson extends StatefulWidget {
final Function addTx;
NewPerson(this.addTx);
#override
_NewPersonState createState() => _NewPersonState();
}
class _NewPersonState extends State<NewPerson> {
final _nameController = TextEditingController();
void _submitData() {
final name = _nameController.text;
widget.addTx(
name
);
Navigator.of(context).pop();
}
#override
Widget build(BuildContext context) {
return Card(
elevation: 5,
child: Container(
padding: EdgeInsets.all(10),
child: Column(
crossAxisAlignment: CrossAxisAlignment.end,
children: <Widget>[
TextField(
decoration: InputDecoration(labelText: 'Name'),
controller: _nameController,
onSubmitted: (_) => _submitData(),
),
RaisedButton(
child: Text('Add Person'),
color: Theme.of(context).primaryColor,
textColor: Theme.of(context).textTheme.button.color,
onPressed: _submitData,
),
],
),
),
);
}
}

You could use this functions to persist and load data from shared preferences.
Get SharedPreferences from here.
To persist data to SharedPreferences, called after adding or deleting a new element to the list.
_persistData() async {
SharedPreferences preferences = await SharedPreferences.getInstance();
await preferences.setStringList("persons", _people);
}
To load data from SharedPreferences, usually called in initState.
_loadData() async {
SharedPreferences preferences = await SharedPreferences.getInstance();
setState(() {
_people = preferences.getStringList("persons");
});
}

How to Set Timer Countdown in Flutter for 30 Second with OnPressed FAB Button?

Currently, I have write codes for making up the counter app with two buttons. 1 raised button to reset and one fab button for increment counter.
is it possible to add the countdown timer to implement on FAB button? When FAB button clicks 20-second countdown timer start.
Also, I have found below thread for the same type of function implement. But I don't where to put codes in my app to implement countdown work on FAB button.
How to make a countdown in flutter?
import 'package:flutter/material.dart';
import 'dart:ui';
void main() => runApp(MyApp());
class MyApp extends StatelessWidget {
#override
Widget build(BuildContext context) {
return MaterialApp(
title: 'Counter App',
theme: ThemeData(
primarySwatch: Colors.blue,
),
home: MyHomePage(title: 'Counter App'),
);
}
}
class MyHomePage extends StatefulWidget {
MyHomePage({Key key, this.title}) : super(key: key);
final String title;
#override
_MyHomePageState createState() => _MyHomePageState();
}
class _MyHomePageState extends State<MyHomePage> with TickerProviderStateMixin {
int _counter = 0;
AnimationController controller;
bool _isButtonDisabled;
Duration get duration => controller.duration * controller.value;
bool get expired => duration.inSeconds == 0;
#override
void initState() {
controller = AnimationController(
vsync: this,
duration: Duration(seconds: 20),
);
super.initState();
}
#override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text(widget.title),
),
body: Center(
child: new Column(
mainAxisAlignment: MainAxisAlignment.center,
children: <Widget>[
Text(
'number $_counter added',
),
AnimatedBuilder(
animation: controller,
builder: (BuildContext context, Widget child) {
return new Text(
'${duration.inSeconds}',
style: new TextStyle(
fontWeight: FontWeight.bold,
fontSize: 50.0,
),
);
}),
new Row(
mainAxisAlignment: MainAxisAlignment.spaceEvenly,
children: <Widget>[
new RaisedButton(
padding: const EdgeInsets.all(15.0),
textColor: Colors.white,
color: Colors.redAccent,
onPressed: () {
setState(() {
controller.reset();
_counter = 0;
});
},
child: new Text("Reset"),
),
new RaisedButton(
onPressed: () => setState(() {
controller.reverse(from: 1);
}),
textColor: Colors.white,
color: Colors.purple,
padding: const EdgeInsets.all(15.0),
child: new Text(
"Start",
),
),
],
),
],
),
),
bottomNavigationBar: BottomAppBar(
child: Container(
height: 50.0,
),
),
floatingActionButton: FloatingActionButton(
onPressed: () => setState(() {
_counter++;
}),
tooltip: 'Increment Counter',
child: Icon(Icons.add),
),
floatingActionButtonLocation: FloatingActionButtonLocation.centerDocked,
);
}
}

you can use anywhere this code.
Timer(Duration(seconds: 30), () {
//checkFirstSeen(); your logic
});

try the following:
import 'package:flutter/material.dart';
import 'dart:ui';
import 'dart:async';
void main() => runApp(MyApp());
class MyApp extends StatelessWidget {
#override
Widget build(BuildContext context) {
return MaterialApp(
title: 'Counter App',
theme: ThemeData(
primarySwatch: Colors.blue,
),
home: MyHomePage(title: 'Counter App'),
);
}
}
class MyHomePage extends StatefulWidget {
MyHomePage({Key key, this.title}) : super(key: key);
final String title;
#override
_MyHomePageState createState() => _MyHomePageState();
}
class _MyHomePageState extends State<MyHomePage> with TickerProviderStateMixin {
int _counter = 0;
AnimationController controller;
Duration get duration => controller.duration * controller.value;
bool get expired => duration.inSeconds == 0;
#override
void initState() {
controller = AnimationController(
vsync: this,
duration: Duration(seconds: 20),
);
super.initState();
}
#override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text(widget.title),
),
body: Center(
child: new Column(
mainAxisAlignment: MainAxisAlignment.center,
children: <Widget>[
AnimatedBuilder(
animation: controller,
builder: (BuildContext context, Widget child) {
return new Text(
'${duration.inSeconds}',
style: new TextStyle(
fontWeight: FontWeight.bold,
fontSize: 50.0,
),
);
}),
new Row(
mainAxisAlignment: MainAxisAlignment.spaceEvenly,
children: <Widget>[
new RaisedButton(
padding: const EdgeInsets.all(15.0),
textColor: Colors.white,
color: Colors.redAccent,
onPressed: () {
setState(() {
controller.reset();
});
},
child: new Text("Reset"),
),
],
),
],
),
),
bottomNavigationBar: BottomAppBar(
child: Container(
height: 50.0,
),
),
floatingActionButton: FloatingActionButton(
onPressed: () => setState(() {
controller.reverse(from: 1);
}),
tooltip: 'Increment Counter',
child: Icon(Icons.add),
),
floatingActionButtonLocation: FloatingActionButtonLocation.centerDocked,
);
}
}