here I created a model, and try to use the model in the page, but I get an error:
The getter 'sundayIsSelected' was called on null.
Receiver: null
Tried calling: sundayIsSelected
I set the sundayIsSelected in AlarmClock default value is false, why in the TimePickerPage there is still null? thanks!
Here is model code:
class AlarmClock {
bool sundayIsSelected;
//I also tried followings:
//bool sundayIsSelected = false;
AlarmClock({
this.sundayIsSelected = false,
});
}
here is my page code.
class TimePickerPage extends StatefulWidget {
final AlarmClock alarmClock;
const TimePickerPage({Key key, this.alarmClock}) : super(key: key);
#override
_TimePickerPageState createState() => _TimePickerPageState();
}
class _TimePickerPageState extends State<TimePickerPage> {
bool sundayIsSelected;
#override
void initState() {
sundayIsSelected = widget.alarmClock.sundayIsSelected;
}
Widget build(BuildContext context) {
Text(sundayIsSelected),
}
}
It is possible for alarmClock to be null, I will recommend adding required parameter on constructor and properly add others annotations.
class TimePickerPage extends StatefulWidget {
final AlarmClock alarmClock;
const TimePickerPage({Key? key, required this.alarmClock}) : super(key: key);
#override
_TimePickerPageState createState() => _TimePickerPageState();
}
class _TimePickerPageState extends State<TimePickerPage> {
late bool sundayIsSelected;
#override
void initState() {
sundayIsSelected = widget.alarmClock.sundayIsSelected;
super.initState();
}
#override
Widget build(BuildContext context) {
return Text(sundayIsSelected.toString());
}
}
And use it like
final alarmClock = AlarmClock(),
....
TimePickerPage(
alarmClock: alarmClock,
),
// or
TimePickerPage(
alarmClock: AlarmClock(),
)
...
Find more on docs.flutter.dev.
Related
How to solve this error?
The named parameter 'key' is required, but there's no corresponding argument. (Documentation) Try adding the required argument.
error
Future<void> onJoin() async {
// update input validation
setState(() {
_channelController.text.isEmpty
? _validateError = true
: _validateError = false;
});
if (_channelController.text.isNotEmpty) {
await _handleCameraAndMic(Permission.camera);
await _handleCameraAndMic(Permission.microphone);
await Navigator.push(
context,
MaterialPageRoute(
builder: (context) => VideoCall(
channelName: _channelController.text,
role: _role,
),
),
);
}
}
class VideoCall
class VideoCall extends StatefulWidget {
final String channelName;
final ClientRole role;
const VideoCall({Key key, required this.channelName, required this.role})
: super(key: key);
#override
_VideoCallState createState() => _VideoCallState();
}
class _VideoCallState extends State<VideoCall> {
final _users = <int>[];
final _infoStrings = <String>[];
bool muted = false;
late RtcEngine _engine;
#override
void dispose() {
// clear users
_users.clear();
// destroy sdk
_engine.leaveChannel();
_engine.destroy();
super.dispose();
}
#override
void initState() {
super.initState();
// initialize agora sdk
initialize();
}
this is the videoCall class in there no any error shows.
when add "key" show this
When remove required property from key in video call class
show this error
In VideoCall class, key property set as a required, change it to optional:
class VideoCall extends StatefulWidget {
final String? channelName;
final ClientRole? role;
const VideoCall({Key? key, this.channelName, this.role})
: super(key: key);
#override
_VideoCallState createState() => _VideoCallState();
}
I'm new to Riverpod and am trying to migrate an app over from Provider. If I had a TextField and wanted to set its value based on my Provider model, I would do this:
class MyWidget extends StatefulWidget{
const MyWidget({ Key? key }) : super(key: key);
#override
State<MyWidget> createState() => _MyWidgetState();
}
class _MyWidgetState extends State<MyWidget> {
var controller = TextEditingController();
#override
void didChangeDependencies() {
super.didChangeDependencies();
//Set the value here...
var model = Provider.of<Model>(context);
controller.text = model.name;
}
Widget build(BuildContext context) {
return TextField(controller: controller)
}
}
As I understand it, didChangeDependencies() would listen to changes from Provider.of<Model>(context) and update my controller accordingly.
I'm trying to pull off the same thing with Provider, but I can't ever get the TextField's value to show up.
class MyWidget extends ConsumerStatefulWidget {
const MyWidget({Key? key}) : super(key: key);
#override
ConsumerState<ConsumerStatefulWidget> createState() => _MyWidgetState();
}
class _MyWidgetState extends ConsumerState<MyWidget> {
var controller = TextEditingController();
#override
void didChangeDependencies() {
super.didChangeDependencies();
//Trying the same thing here...
final name = ref.watch(providerName);
controller.text = name;
}
Widget build(BuildContext context) {
final name = ref.watch(providerName);
return Column(
children: [
//This doesn't work:
TextField(controller: controller),
//I know my provider has the value, because this works fine:
Text(name),
]
}
}
How can I get my TextEditingController's text property to update?
From Riverpod official website
///1.Create a [StateNotifier] sub-class, StateNotifier is something where you can define functions that can change your state like in this state is of String type, you also can use objects (Classes instead of primitive types)
class Counter extends StateNotifier<String> {
Counter() : super('');
void changeText(String text){
state=text;
}
///2.Create a provider [StateNotifierProvider] with this you can use in your widget
final counterProvider = StateNotifierProvider<Counter, String>((ref) {
return Counter();
});
///3.Consume the Provider this is how we can attach state with our widget
class Home extends ConsumerWidget {
#override
Widget build(BuildContext context, WidgetRef ref) {
final text = ref.watch(counterProvider);
return Text('$text');
}
}
so here you can add you widget like button and onTap executes the code like
onTap()=>changeText(textController.text);
So your text [Text('$text');] will automatically change.
String inputText = controller.text;
Why does not generic Future<T> assign work? i Get this error: A value of type 'Future<T>?' can't be assigned to a variable of type 'Future<T>?'.
typedef SimpleFutureFunction<T> = Widget Function(void Function(Future<T>? newFuture) onFuture);
class SimpleFuture<T> extends StatefulWidget {
const SimpleFuture({Key? key, required this.simple, this.future}) : super(key: key);
final SimpleFutureFunction simple;
final Future<T>? future;
#override
State<SimpleFuture> createState() => _SimpleFutureState();
}
class _SimpleFutureState<T> extends State<SimpleFuture<T>> {
Future<T>? _future;
#override
void initState() {
super.initState();
_future = widget.future;
}
#override
Widget build(BuildContext context) {
return widget.simple.call(<T>(Future<T>? newFuture) {
setState(() {
_future = newFuture;
});
});
}
}
It's the first time a use Flutter (2.8.1) and I'having problems trying to undestrand what's going wrong.
I have a Stateful widget like this:
class SimpleWidget extends StatefulWidget {
const SimpleWidget({Key key, #required this.aValue}) : super(key: key);
final Type2 aValue;
#override
_SimpleWidgetState createState() => _SimpleWidgetState();
}
class _SimpleWidgetState extends State<SimpleWidget> {
Type1 from;
Type1 to;
#override
void initState() {
print('mounted: $mounted'); // true
print('widget.aValue: ${widget.aValue}'); // null <-- WHY IS THIS NULL?
super.initState();
from = ...;
to = ...;
}
...
}
that I call in this way:
List<Type1> breakTimes = await showDialog(
context: context,
builder: (context) {
print('currentElement.aValue: ${currentElement.aValue}'); // not null
return SimpleWidget(aValue: currentElement.aValue);
},
);
Why is widget.aValue == null in initInstance()? How can I solve it?
There is wrong in your code :
Chane this to this:
class SimpleWidget extends StatefulWidget {
final Type2 aValue; // initialize 1st
const SimpleWidget({Key key, #required this.aValue}) : super(key: key);
#override
_SimpleWidgetState createState() => _SimpleWidgetState();
}
In my flutter app I created variables var from, to; and pass those with their values to the next page. which I used it with the widget.from & widget.to.
but how can i pass this widget.from & widget.to variables to var newFrom, newTo; these variables?
class FirstPage extends StatelessWidget {
#override
Widget build(BuildContext context) {
var from = "Five", to = "Ten";
return SecondPage(from: from, to: to);
}
}
class SecondPage extends StatefulWidget {
final from, to;
const SecondPage({Key key, this.from, this.to}) : super(key: key);
#override
_SecondPageState createState() => _SecondPageState();
}
class _SecondPageState extends State<SecondPage> {
var newFrom = "", newTo = "";
#override
void initState() {
setState(() {
newFrom = widget.from;
newTo = widget.to;
});
super.initState();
}
#override
Widget build(BuildContext context) {
return Container(
child: Text("$newFrom $newTo"),
);
}
}