this is my code, i dont know how to pass this listOfTiles to my StatefulWidget, can u help me and describe how it works?
body: new ListView.builder(
itemBuilder: (BuildContext context, int index) {
return new StuffInTilesState(listOfTiles[index]);//i want to pass this
},
itemCount: listOfTiles.length,
),
),
);
}
}
class StuffInTiles extends StatefulWidget{
#override
StuffInTilesState createState() => StuffInTilesState();//i know i need to change this, but i dont know how
}
class StuffInTilesState extends State<StuffInTiles> {
final MyTile myTile;
StuffInTilesState(this.myTile);//this is constructor, shuld this also be changed?
final _controller = TextEditingController();
String name = "";
If u want to see my working code: https://pastebin.pl/view/c4dbc2af If u want to see my not working code: https://pastebin.pl/view/83f9cad0 (https://codeshare.io/GLLm66)
You need to use the widget class constructor and not the state class.
You can access the values in the state class with widget.YouProperty
class StuffInTiles extends StatefulWidget {
final MyTile myTile;
const StuffInTiles(this.myTile);
#override
_StuffInTilesState createState() => _StuffInTilesState();
}
class _StuffInTilesState extends State<StuffInTiles> {
#override
Widget build(BuildContext context) {
return Container(child:
Text(widget.myTile),);
}
}
Related
I have faced with strange behavior of extensions of abstract class in the Dart.
The Code
I have following files:
BaseListItem.dart
abstract class BaseListItem {
ImageProvider get _icon;
IHealthChecker get _healthChecker;
String get _name;
String get _unit;
Widget build(BuildContext context) {
... build widgets tree ...
}
}
Temperature.dart
class Temperature extends BaseListItem {
#override
IHealthChecker get _healthChecker => TemperatureHealthChecker();
#override
ImageProvider<Object> get _icon => const Svg('assets/images/icons/Temperature.svg');
#override
String get _name => "Temperature";
#override
String get _unit => "°C";
}
And all this inheritance stuff I am using in SensorsList.dart file.
class SensorsList extends StatefulWidget {
#override
State<StatefulWidget> createState() => _StateSensorsList();
}
class _StateSensorsList extends State<SensorsList> {
final List<BaseListItem> sensors = [Temperature(), Humidity()];
#override
Widget build(BuildContext context) {
return ListView.builder(
itemCount: sensors.length,
shrinkWrap: true,
itemBuilder: (BuildContext context, int index) {
return sensors[index].build(context);
});
}
}
The problem
This code built but fail at run time with next exception
Exception has occurred.
NoSuchMethodError (NoSuchMethodError: Class 'Temperature' has no instance getter '_icon'.
Receiver: Instance of 'Temperature'
Tried calling: _icon)
❗️The problem disappears if I put abstract class BaseListItem and his extension Temperature into a single file.❗️
The reason why it happens is because the variables are private. Private variables can only be accessed within the same file. See also In Dart, how to access a parent private var from a subclass in another file?
Get variable data from a Stateful widget in another Stateful widget and they have no relation to one another (They are not children nor parents to each other)
I want to be able to access an array (posts) that is located in another file... You can see the comments in the code for more information
I have this stateful widget
import 'package:flutter/material.dart';
import 'package:saviortv/modules/fetchPosts.dart';
import 'package:saviortv/ui/BuildPost.dart';
class Home extends StatefulWidget {
#override
_HomeState createState() => _HomeState();
}
class _HomeState extends State<Home> {
#override
Widget build(BuildContext context) {
return ListView.builder(
itemCount: posts == null ? 0 : posts.length, // <== here posts is undefined because it doesn't exist as I want to get it from the other file (See below)
itemBuilder: (BuildContext context, int index) {
return buildPost(context, posts, index); //Building the posts list view
},
);
}
}
The other Stateful widget
class FetchPosts extends StatefulWidget {
FetchPosts({Key key, this.pageNumber = 1}) : super(key: key);
final int pageNumber;
#override
_FetchPostsState createState() => _FetchPostsState(pageNumber);
}
class _FetchPostsState extends State<FetchPosts> {
_FetchPostsState(this.pageNumber);
int pageNumber;
List<wp.Post> posts = []; //<== I want this to be useable in the other file;
Future<String> getPosts() async {
var res = await fetchPosts(pageNumber);
print(pageNumber);
setState(() {
posts = res;
});
return "Success!";
}
// Get _ when app loads;
#override
void initState() {
super.initState();
this.getPosts();
}
#override
Widget build(BuildContext context) {
return Container();
}
}
How can I achieve that?
I am unable to access a public static boolean from a different class, eg. I have a boolean isFull in my StudyjiosListviewScreen class as shown:
class StudyjiosListviewScreen extends StatefulWidget {
#override
_StudyjiosListviewScreenState createState() => _StudyjiosListviewScreenState();
}
class _StudyjiosListviewScreenState extends State<StudyjiosListviewScreen> {
static bool isFull = false;
...
I want to use this boolean isFull in another class JoinStudyjio.
I created an instance of the StudyjiosListviewScreen class in the JoinStudyjio class like this:
StudyjiosListviewScreen listviewScreen = StudyjiosListviewScreen();
But when I try to use the boolean isFull like this:
if (listviewScreen.isFull) {
...
I get an error. I have already imported the file for the StudyjiosListviewScreen class inside the file for the JoinStudyjio class.
This is because StudyjiosListviewScreen and _StudyjiosListviewScreenState are 2 different classes.
The static variable isFull which you are trying to access is of the later one and you are trying to access it by creating an instance of the first one. If it had been a static variable of the class StudyjiosListviewScreen, you could have accessed it without even creating an instance of that class like this StudyjiosListviewScreen.isFull
If I understood your issue correctly, and following the suggestion I made in my comment, here is a code example of sharing a variable and a method to change it's value, down to two classes from a parent class:
class VariableSharing62951032 extends StatefulWidget {
#override
_VariableSharing62951032State createState() => _VariableSharing62951032State();
}
class _VariableSharing62951032State extends State<VariableSharing62951032> {
bool isFull = false;
#override
Widget build(BuildContext context) {
return Column(
children: <Widget>[
ClassA62951032(isFull: isFull, swapIsFull: swapIsFull,),
ClassB62951032(isFull: isFull, swapIsFull: swapIsFull,),
],
);
}
void swapIsFull(){
setState(() {
isFull = !isFull;
});
}
}
class ClassA62951032 extends StatefulWidget {
final bool isFull;
final Function swapIsFull;
ClassA62951032({
this.isFull,
this.swapIsFull
});
#override
_ClassA62951032State createState() => _ClassA62951032State();
}
class _ClassA62951032State extends State<ClassA62951032> {
#override
Widget build(BuildContext context) {
return Column(
children: <Widget>[
Text('Class A'),
Text(widget.isFull.toString()),
RaisedButton(
child: Text('Swap isFull'),
onPressed: () => widget.swapIsFull(),
),
],
);
}
}
class ClassB62951032 extends StatefulWidget {
final bool isFull;
final Function swapIsFull;
ClassB62951032({
this.isFull,
this.swapIsFull
});
#override
_ClassB62951032State createState() => _ClassB62951032State();
}
class _ClassB62951032State extends State<ClassB62951032> {
#override
Widget build(BuildContext context) {
return Column(
children: <Widget>[
Text('Class B'),
Text(widget.isFull.toString()),
RaisedButton(
child: Text('Swap isFull'),
onPressed: () => widget.swapIsFull(),
),
],
);
}
}
Sharing variables and methods between classes it's a huge deal in Flutter.
First of all, you are passing it in the wrong way. That variable is saved in your state widget, which is defined as private.
So, or you define it as public and than you pass a key associated with your state, or you change complitelly approach. I don't like passing keys and it is not good for production, so I will give you a better example using providers:
add provider library to your pubspec.yaml:
provider: ^4.3.1 // Or latest version
Create a class where you can save that value:
class valuesHelper {
//In this class we are storing global, dynamic values
bool _isSeen;
valuesHelper() {
this._isSeen = false;
}
void setValue(bool value) {
this._isSeen = value;
}
bool getValue(){
return this._isSeen;
}
}
Now wrap your main with the provider and pass the valuesHelper();
class MyApp extends StatelessWidget {
// This widget is the root of your application.
#override
Widget build(BuildContext context) {
return Provider(
create: (_) => valuesHelper(),
child: MaterialApp(
home: MyHomePage(),
),
);
}
}
Now call the Provider.of(context) wherever you want.
//Somwhere in your code when you have access to context:
ValueHelper helper = Provider.of<valueHelper>(context);
helper.setValue(true);
//Somwhereelse in your code when you have access to context:
ValueHelper helper = Provider.of<valueHelper>(context);
bool theValueIWant = helper.getValue();
If you have asynchronous stuff and huge state managment Blocs are even better and fancier, but for this kind of things Providers are more than enough.
I'm trying to access the information I've passed over from a previous class before the build method begins. But it's saying only static members can be accessed in initializers. I don't really want to use the static property, partially because I wouldn't know how to use it, but also because I think it seems unnecessary. In previous pages I've been able to access the data but only after the build method, does anyone know how I can access it before? Thanks all
class FirstPage extends StatefulWidget {
#override
_FirstPageState createState() => _FirstPageState();
}
class _FirstPageState extends State<FirstPage> {
List<MyProvider> myList;
#override
Widget build(BuildContext context) {
return Scaffold(
body: ListView.builder(
itemCount: myList.length,
itemBuilder: (context, index) {
String imgPath = myList[index].image;
String myTextPath = myList[index].name;
String locationNamePath = myList[index].location;
double distancePath = myList[index].distance;
String myName = '${myTextPath} ''${locationNamePath}';
return MyCard(
locationText: locationNamePath,
myText: myTextPath,
assetImage: Image.network(imgPath),
function: (){
Provider.of<Data>(context, listen: false).addLogo(Image.network(imgPath));
Navigator.push(context, MaterialPageRoute(builder: (context) => SecondPage(myName: myName,)));
},
);
}),
);
}
}
My next page accesses the data using a key but it seems not to be able to use it before the build method, and that's what I need to get around!
class SecondPage extends StatefulWidget {
final String myName;
const SecondPage({Key key, this.myName})
: super(key: key);
#override
_SecondPageState createState() => _SecondPageState();
}
class _SecondPageState extends State<SecondPage> with TickerProviderStateMixin {
final CollectionReference myItemsReference = Firestore.instance.collection('${widget.myName}');
// This is where the error is
#override
Widget build(BuildContext context) {
return Scaffold();
}
}
Use the initState method for anything related to initialization of State. See this for more on initState.
Example:
CollectionReference myItemsReference;
#override
void initState() {
myItemsReference = Firestore.instance.collection('${widget.myName}');
}
I have 2 screens in my Flutter app: a list of records and a screen for creating and editing records.
If I pass an object to the second screen that means I am going to edit this and if I pass null it means that I am creating a new item. The editing screen is a Stateful widget and I am not sure how to use this approach https://flutter.io/cookbook/navigation/passing-data/ for my case.
class RecordPage extends StatefulWidget {
final Record recordObject;
RecordPage({Key key, #required this.recordObject}) : super(key: key);
#override
_RecordPageState createState() => new _RecordPageState();
}
class _RecordPageState extends State<RecordPage> {
#override
Widget build(BuildContext context) {
//.....
}
}
How can I access recordObject inside _RecordPageState?
To use recordObject in _RecordPageState, you have to just write widget.objectname like below
class _RecordPageState extends State<RecordPage> {
#override
Widget build(BuildContext context) {
.....
widget.recordObject
.....
}
}
Full Example
You don't need to pass parameters to State using it's constructor.
You can easily access these using widget.myField.
class MyRecord extends StatefulWidget {
final String recordName;
const MyRecord(this.recordName);
#override
MyRecordState createState() => MyRecordState();
}
class MyRecordState extends State<MyRecord> {
#override
Widget build(BuildContext context) {
return Text(widget.recordName); // Here you direct access using widget
}
}
Pass your data when you Navigate screen :
Navigator.of(context).push(MaterialPageRoute(builder: (context) => MyRecord("WonderWorld")));
class RecordPage extends StatefulWidget {
final Record recordObject;
RecordPage({Key key, #required this.recordObject}) : super(key: key);
#override
_RecordPageState createState() => new _RecordPageState(recordObject);
}
class _RecordPageState extends State<RecordPage> {
Record recordObject
_RecordPageState(this. recordObject); //constructor
#override
Widget build(BuildContext context) {. //closure has access
//.....
}
}
example as below:
class nhaphangle extends StatefulWidget {
final String username;
final List<String> dshangle;// = ["1","2"];
const nhaphangle({ Key key, #required this.username,#required this.dshangle }) : super(key: key);
#override
_nhaphangleState createState() => _nhaphangleState();
}
class _nhaphangleState extends State<nhaphangle> {
TextEditingController mspController = TextEditingController();
TextEditingController soluongController = TextEditingController();
final scrollDirection = Axis.vertical;
DateTime Ngaysx = DateTime.now();
ScrollController _scrollController = new ScrollController();
ApiService _apiService;
List<String> titles = [];
#override
void initState() {
super.initState();
_apiService = ApiService();
titles = widget.dshangle; //here var is call and set to
}
I have to Navigate back to any one of the screens in the list pages but when I did that my onTap function stops working and navigation stops.
class MyBar extends StatefulWidget {
MyBar({this.pageNumber});
final pageNumber;
static const String id = 'mybar_screen';
#override
_MyBarState createState() => _MyBarState();
}
class _MyBarState extends State<MyBar> {
final List pages = [
NotificationScreen(),
AppointmentScreen(),
RequestBloodScreen(),
ProfileScreen(),
];
#override
Widget build(BuildContext context) {
var _selectedItemIndex = widget.pageNumber;
return Scaffold(
bottomNavigationBar: BottomNavigationBar(
elevation: 0,
backgroundColor: Colors.white,
unselectedItemColor: Colors.grey.shade700,
selectedItemColor: Color(kAppColor),
selectedIconTheme: IconThemeData(color: Color(kAppColor)),
currentIndex: _selectedItemIndex,
type: BottomNavigationBarType.fixed,
onTap: (int index) {
setState(() {
_selectedItemIndex = index;
});
},
You should use a Pub/Sub mechanism.
I prefer to use Rx in many situations and languages. For Dart/Flutter this is the package: https://pub.dev/packages/rxdart
For example, you can use a BehaviorSubject to emit data from widget A, pass the stream to widget B which listens for changes and applies them inside the setState.
Widget A:
// initialize subject and put it into the Widget B
BehaviorSubject<LiveOutput> subject = BehaviorSubject();
late WidgetB widgetB = WidgetB(deviceOutput: subject);
// when you have to emit new data
subject.add(deviceOutput);
Widget B:
// add stream at class level
class WidgetB extends StatefulWidget {
final ValueStream<LiveOutput> deviceOutput;
const WidgetB({Key? key, required this.deviceOutput}) : super(key: key);
#override
State<WidgetB> createState() => _WidgetBState();
}
// listen for changes
#override
void initState() {
super.initState();
widget.deviceOutput.listen((event) {
print("new live output");
setState(() {
// do whatever you want
});
});
}
In my app, often instead of using stateful widgets, I use mainly ChangeNotifierProvider<T> in main.dart, some model class
class FooModel extends ChangeNotifier {
var _foo = false;
void changeFooState() {
_foo = true;
notifyListeners();
}
bool getFoo () => _foo;
}
and
var foo = context.read<FooModel>();
# or
var foo = context.watch<FooModel>();
in my stateless widgets. IMO this gives me more precise control over the rebuilding upon runtime state change, compared to stateful widgets.
The recipe can be found in the official docs, the concept is called "lifting state up".