Develop Reference

How can i add delay between items in listview.builder?

I have a ListView containing string items. I want to make it so that ListView's items show one by one with delay. And after each item appears, I want to wait about 2 seconds with a typing indicator and then the next item will appear. How will I do? Please give me the solution. Thanks!

You can use AnimatedListView like this code below
https://www.youtube.com/watch?v=ZtfItHwFlZ8
// main.dart
import 'package:flutter/material.dart';
void main() {
runApp(const MyApp());
}
class MyApp extends StatelessWidget {
const MyApp({Key? key}) : super(key: key);
#override
Widget build(BuildContext context) {
return MaterialApp(
debugShowCheckedModeBanner: false,
title: 'Test',
theme: ThemeData(
primaryColor: Colors.green,
colorScheme:
ColorScheme.fromSwatch().copyWith(secondary: Colors.greenAccent)),
home: const HomePage(),
);
}
}
class HomePage extends StatefulWidget {
const HomePage({Key? key}) : super(key: key);
#override
_HomePageState createState() => _HomePageState();
}
class _HomePageState extends State<HomePage> {
// Items in the list
final _items = ["Item 0"];
// The key of the list
final GlobalKey<AnimatedListState> _key = GlobalKey();
// Add a new item to the list
// This is trigger when the floating button is pressed
void _addItem() {
_items.insert(0, "Item ${_items.length + 1}");
_key.currentState!.insertItem(0, duration: const Duration(seconds: 1));
}
// Remove an item
// This is trigger when an item is tapped
void _removeItem(int index, BuildContext context) {
AnimatedList.of(context).removeItem(index, (_, animation) {
return FadeTransition(
opacity: animation,
child: SizeTransition(
sizeFactor: animation,
child: SizedBox(
height: 150,
child: Card(
margin: const EdgeInsets.symmetric(vertical: 20),
elevation: 10,
color: Colors.red[400],
child: const Center(
child: Text("I am going away",
style: const TextStyle(fontSize: 28)),
),
),
),
),
);
}, duration: const Duration(seconds: 1));
_items.removeAt(index);
}
#override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: const Text('Test list'),
actions: [
IconButton(
onPressed: _addItem,
icon: const Icon(Icons.plus_one_outlined),
)
],
),
body: AnimatedList(
key: _key,
initialItemCount: 1,
padding: const EdgeInsets.all(10),
itemBuilder: (context, index, animation) {
return SlideTransition(
key: UniqueKey(),
position: Tween<Offset>(
begin: const Offset(-1, -0.5),
end: const Offset(0, 0),
).animate(animation),
child: RotationTransition(
turns: animation,
child: SizeTransition(
axis: Axis.vertical,
sizeFactor: animation,
child: SizedBox(
height: 150,
child: InkWell(
onTap: () => _removeItem(index, context),
child: Card(
margin: const EdgeInsets.symmetric(vertical: 20),
elevation: 10,
color: Colors.primaries[
(index * 100) % Colors.primaries.length][300],
child: Center(
child: Text(_items[index],
style: const TextStyle(fontSize: 28)),
),
),
),
),
),
),
);
},
),
);
}
}

Try wrapping your widget around this widget https://pub.dev/packages/delayed_display. Please confirm if this works.

How to bring widgets to next line in ListViewBuilder? flutter

ive been using flutter for past few months and now ive stuck in a problem where i get a list of tag names and i have to design a ui to show the tags to user as the image given below.
,
when i use ListViewBuilder and Row to display the tags as it renders all the widgets in the stragint line i get renderfelx overflow error as shown in the image below..
This is how my code looks-
Container(
height: 40,
child: ListView.builder(
shrinkWrap: true,
itemCount: brandmodels[index].tags.length,
itemBuilder: (context, index0) {
return Row(
children: [
Padding(
padding: const EdgeInsets.all(8.0),
child: CircleAvatar(
radius: 05,
backgroundColor: Color(0xffC4C4C4)),
),
Padding(
padding:
const EdgeInsets.only(right: 8.0),
child: Expanded(
child: Text(
brandmodels[index].tags[index0],
),
),
),
],
);
},
),
)
So how to bring the widgets to next line when it hits the maximum width of the screen?.

I just changed ListView to Wrap widget.
(To check whether there is overflow issue, I set Container's width to 300.
And give a background color for checking Container area.)
import 'package:flutter/material.dart';
void main() {
runApp(MyApp());
}
class MyApp extends StatelessWidget {
#override
Widget build(BuildContext context) {
return MaterialApp(
title: 'Flutter Demo',
theme: ThemeData(
primarySwatch: Colors.blue,
visualDensity: VisualDensity.adaptivePlatformDensity,
),
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
void initState() {
super.initState();
}
#override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text(widget.title),
),
body: _buildBody(),
floatingActionButton: FloatingActionButton(
onPressed: () {},
tooltip: 'Increment',
child: Icon(Icons.add),
),
);
}
Widget _buildBody() {
List data = ['biscuits', 'cakes', 'drinks', 'snacks', 'food'];
return Container(
color: Colors.yellow[100],
height: 60,
width: 300,
child: Wrap(
direction: Axis.horizontal,
children: data.map((item) {
return Row(
mainAxisSize: MainAxisSize.min,
children: [
Padding(
padding: const EdgeInsets.all(8.0),
child: CircleAvatar(
radius: 05, backgroundColor: Color(0xffC4C4C4)),
),
Padding(
padding: const EdgeInsets.only(right: 8.0),
child: Expanded(
child: Text(
item,
),
),
),
],
);
}).toList(),
),
);
}
}

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]),
),
);
}

Flutter Slider (activeTrackHeight and inactiveTrackHeight)

Why activeTrackHeight and inactiveTrackHeight length are different ?
I hope they are the same length.
How do I fix my code ?
please help.
I use Android studio 4.0
and Flutter 1.22.3
I tried some custom slider packages and searched for solutions in search engines, but couldn't find one.
sorry my poor English.
import 'package:flutter/material.dart';
void main() {
runApp(MyApp());
}
class MyApp extends StatelessWidget {
#override
Widget build(BuildContext context) {
return MaterialApp(
title: 'Flutter Demo',
theme: ThemeData(
sliderTheme: SliderThemeData(
trackHeight: 14,
thumbColor: Colors.white,
thumbShape: RoundSliderThumbShape(enabledThumbRadius: 7),
valueIndicatorColor: Colors.orange,
overlayColor: Colors.transparent,
activeTrackColor: Colors.black,
activeTickMarkColor: Colors.red,
inactiveTrackColor: Colors.black,
inactiveTickMarkColor: Colors.grey,
),
),
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> {
double val=1;
#override
Widget build(BuildContext context) {
return Scaffold(
body: Center(
child: Column(
mainAxisAlignment: MainAxisAlignment.center,
children: <Widget>[
Text(
'activeTrackHeight and inactiveTrackHeight',
),
Container(
width: 140,
height: 240,
child: Transform.scale(
scale: 4.0,
child: Slider(
value: val,
min: 0,
max: 2,
divisions: 2,
onChanged: (double value) {
setState (() {
val = value;
});
},
),
),
),
],
),
),
);
}
}

Add trackShape: RectangularSliderTrackShape() to your SliderThemeData:
class MyApp extends StatelessWidget {
#override
Widget build(BuildContext context) {
return MaterialApp(
title: 'Flutter Demo',
theme: ThemeData(
sliderTheme: SliderThemeData(
trackShape: RectangularSliderTrackShape(),
trackHeight: 14,
thumbColor: Colors.white,
thumbShape: RoundSliderThumbShape(enabledThumbRadius: 7),
valueIndicatorColor: Colors.orange,
overlayColor: Colors.transparent,
activeTrackColor: Colors.black,
activeTickMarkColor: Colors.red,
inactiveTrackColor: Colors.black,
inactiveTickMarkColor: Colors.grey,
),
),
home: MyHomePage(title: 'Flutter Demo Home Page'),
);
}
}

Black-Screen with the FlatButton in the AppBar

My App contains basically 2 parts -> Appbar (with 1 Button) and BottomNavigationBar (with some buttons that works properly). The problem came when I pressed the Appbar button (goes to a black screen instead of show the "manual_page.dart")
this is the content of the 2 files (the home_page.dart and manual_page.dart):
home_page.dart
import 'package:flutter/material.dart';
import 'package:opening_a_pdf/manual_page.dart';
import 'package:opening_a_pdf/first_page.dart';
import 'package:opening_a_pdf/second_page.dart';
class MyHomePage extends StatefulWidget {
MyHomePage({Key key, this.title}) : super(key: key);
final String title;
#override
_MyHomePageState createState() => _MyHomePageState();
}
class _MyHomePageState extends State<MyHomePage> {
int _selectedPage = 0;
List<Widget> pageList = List<Widget>();
#override
void initState() {
pageList.add(FirstPage());
pageList.add(SecondPage());
super.initState();
}
#override
Widget build(BuildContext context) {
return Scaffold(
backgroundColor: Color(0xFFFAFAFA),
appBar: AppBar(
backgroundColor: Colors.black,
title: const Text('Aplicación en Desarrollo'),
actions: <Widget>[
FlatButton(
textColor: Colors.white,
child: Text(
'MANUAL',
style: TextStyle(
fontSize: 16.0,
fontWeight: FontWeight.bold,
),
),
onPressed: (){
Navigator.push(
context,
MaterialPageRoute(builder: (context) => Voice()),
);
}
)
],
),
body: IndexedStack(
index: _selectedPage,
children: pageList,
),
bottomNavigationBar: BottomNavigationBar(
// type: BottomNavigationBarType.fixed,
items: const <BottomNavigationBarItem>[
BottomNavigationBarItem(
backgroundColor: Colors.black,
icon: Icon(Icons.compare_arrows),
title: Text('Conectividad'),
),
BottomNavigationBarItem(
backgroundColor: Colors.black,
icon: Icon(Icons.blur_on),
title: Text('Captura Datos'),
),
BottomNavigationBarItem(
backgroundColor: Colors.black,
icon: Icon(Icons.graphic_eq),
title: Text('Voz'),
),
BottomNavigationBarItem(
backgroundColor: Colors.black,
icon: Icon(Icons.list),
title: Text('Comandos'),
),
BottomNavigationBarItem(
backgroundColor: Colors.black,
icon: Icon(Icons.settings),
title: Text('Ajustes'),
),
],
currentIndex: _selectedPage,
selectedItemColor: Colors.amber[800],
onTap: _onItemTapped,
), // This trailing comma makes auto-formatting nicer for build methods.
);
}
void _onItemTapped(int index) {
setState(() {
_selectedPage = index;
});
}
}
manual_page.dart
import 'package:flutter/material.dart';
// ignore: camel_case_types
class Voice extends StatelessWidget {
#override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text("Sección de Órdenes por Voz"),
),
body: Stack(
fit: StackFit.expand,
children: <Widget>[
Positioned(
bottom: 0,
width: MediaQuery.of(context).size.width,
child: Center(
child: MaterialButton(
onPressed: () {},
color: Colors.red,
),
),
)
],
),
);
}
}

Try to initial the height of container in the second screen before Stack

There are no errors in the code. Works correctly. Maybe the fault is in the main () or in the emulator.
Code in main:
void main() {
runApp(MyApp());
}
class MyApp extends StatelessWidget {
// This widget is the root of your application.
#override
Widget build(BuildContext context) {
return MaterialApp(
home: MyHomePage(title: 'Flutter Demo Home Page'),
);
}
}

I executed your code and found no problem with it:
But you can put empty Container() as the child of MaterialButton().
Corrected code:
MaterialButton(
onPressed: () {},
color: Colors.red,
child:Container(),
),