My App is disposing a controller everytime I leave the page, however, I am not initializing the controller with initState() and am initializing it onTap, so I was wondering if it is possible to check if the controller has been initialized to figure out if it should dispose it or not.
The Controller is:
VideoPlayerController _controller;
And I am initializing it after an onTap:
onTap: () {
setState(() {
_initVideo(file);
});
}
_initVideo(Future<File> videoFile) async {
final video = await videoFile;
_controller = VideoPlayerController.file(video)
..setLooping(false)
..initialize().then((value) => setState(() {
_controller.addListener(() {
setState(() {
});
});
}));
}
And for the dispose I am trying to check whether or not the VideoController has been initialized, if it has then dispose(), otherwise don't.
#override
void dispose() {
_controller.dispose();
super.dispose();
}
A simple solution might be to set a flag to true when it's initialized, and check that in your dispose method (I am aware that this should be a comment, but I don't have 50 rep).
you can check if this widget is disposed after initializing video
if you are using StatefulWidget
await videoPlayerController.initialize();
if (!mounted) return;
videoPlayerController.play();
Related
You can see the strange behaviour in this video: https://streamable.com/r5ld2y
The InitValue is the correct one, but when I restart the App it first goes to zero, AFTER loading the Screen OR press a button, it loads the shared prefs...
This is my Cubit (Only with the LoadCounter Func):
class DrinkCubit extends Cubit<DrinkState> {
DrinkCubit() : super(DrinkState(drinkValue: 0));
Future<void> loadCounter() async {
final prefs = await SharedPreferences.getInstance();
state.drinkValue = (prefs.getInt('counter') ?? 0);
}
}
And this is my InitFunction in the main window!
#override
void initState() {
super.initState();
Future.delayed(Duration.zero,()
{
BlocProvider.of<DrinkCubit>(context).loadCounter();
});
}
So how do I fix this, that the correct value is directly after starting the app showed
Try this:
getData(){
BlocProvider.of<DrinkCubit>(context).loadCounter();
}
#override
void initState() {
SchedulerBinding.instance.addPostFrameCallback((_) {
getData();
});
super.initState();
}
SchedulerBinding.instance.addPostFrameCallback ensures that code inside run before UI code.
And if it allows me to give you a hint, is better remove SharedPreferences of your Bloc and put in another class.
So while learning Flutter, it seems that initState() is not a place to use Providers as it does not yet have access to context which must be passed. The way my instructor gets around this is to use the didChangeDependencies() life-cycle hook in conjunction with a flag so that any code inside doesn't run more than once:
bool _isInit = true;
#override
void didChangeDependencies() {
if (_isInit) {
// Some provider code that gets/sets some state
}
_isInit = false;
super.didChangeDependencies();
}
This feels like a poor development experience to me. Is there no other way of running initialisation code within a Flutter Widget that has access to context? Or are there any plans to introduce something more workable?
The only other way I have seen is using Future.delayed which feels a bit "hacky":
#override
void initState() {
Future.delayed(Duration.zero).then(() {
// Some provider code that gets/sets some state
});
super.initState();
}
I have implemented as follows inside didChangeDependencies
#override
void didChangeDependencies() {
super.didChangeDependencies();
if (_isInit) {
setState(() {
_isLoading = true;
});
Provider.of<Products>(context).fetchAndSetProducts().then((_) {
setState(() {
_isLoading = false;
});
});
}
_isInit = false;
}
It's possible to schedule code to run at the end of the current frame. If scheduled within initState(), it seems that the Widget is fully setup by the time the code is running.
To do so, you can use the addPostFrameCallback method of the SchedulerBinding instance:
#override
void initState() {
super.initState();
SchedulerBinding.instance.addPostFrameCallback((_) {
// Some provider code that gets/sets some state
})
}
You can also use WidgetsBinding.instance.addPostFrameCallback() for this. They both behave the same for the purpose of running code once after the Widget has been built/loaded, but here is some more detail on the differences.
Note: be sure to import the file needed for SchedulerBinding:
import 'package:flutter/scheduler.dart';
you can have the Provider in a separate function and call that function within the initState()
bool isInit = true;
Future<void> fetch() async {
await Provider.of<someProvider>(context, listen: false).fetch();
}
#override
void initState() {
if (isInit) {
isInit = false;
fetch();
}
isInit = false;
super.initState();
}
I have a flutter camera app and am able to get a recorded video to play. The problem is, I am only able to get it to play when a button is pressed. How do I get the code to run when the widget(screen) is created instead of when the button is pressed so I don't have to press a button to get it to play? Here is my code:
Here is the code for when the button is pressed:
//raised button
RaisedButton(
onPressed: () {stopButtonPressed();},
//stopButtonPressed
void stopButtonPressed() {
print('stopButtonPressed hit');
stopVideoRecording().then((_) {
print('StopVideoRecording complete');
});
}
//stopVideoRecording
Future<void> stopVideoRecording() async {
print('stopVideoRecording hit');
await _startVideoPlayer();
}
//_startVideoPlayer
Future<void> _startVideoPlayer() async {
print('_startVideoPlayer hit');
print(Provider.of<SendDataModel>(context, listen: false).displayImageVideo());
final VideoPlayerController vcontroller =
VideoPlayerController.file(File(Provider.of<SendDataModel>(context, listen: false).displayImageVideo()));
videoPlayerListener = () {
if (videoController != null && videoController.value.size != null) {
if (mounted) setState(() {});
videoController.removeListener(videoPlayerListener);
}
};
vcontroller.addListener(videoPlayerListener);
await vcontroller.setLooping(true);
await vcontroller.initialize();
await videoController?.dispose();
if (mounted) {
setState(() {
//saveImagePath = null;
videoController = vcontroller;
});
}
await vcontroller.play();
} //startVideoPlayer
Thanks!
You can call the function from initState(). initState() is called only once when the StatefulWidget is inserted into the Widget tree, so it's a good place to initialize variables or do what you're trying to do.
class _MyHomePageState extends State<MyHomePage> {
#override
void initState() {
super.initState();
// Do anything you need done here
_startVideoPlayer();
// If you want a slight delay, use Future.delayed
Future.delayed(Duration(seconds: 1), (){
_startVideoPlayer();
});
}
#override
Widget build(BuildContext context) {
return Scaffold(
// rest of app
I am calling initial method to load data from API using initState. But it is resulting me an error. Here is error:
Unhandled Exception: inheritFromWidgetOfExactType(_LocalizationsScope) or inheritFromElement() was called before _ScreenState.initState() completed.
When an inherited widget changes, for example if the value of Theme.of() changes, its dependent widgets are rebuilt. If the dependent widget's reference to the inherited widget is in a constructor or an initState() method, then the rebuilt dependent widget will not reflect the changes in the inherited widget.
My code is:
#override
void initState() {
super.initState();
this._getCategories();
}
void _getCategories() async {
AppRoutes.showLoader(context);
Map<String, dynamic> data = await apiPostCall(
apiName: API.addUser,
context: context,
parameterData: null,
showAlert: false,
);
if(data.isNotEmpty){
AppRoutes.dismissLoader(context);
print(data);
}else {
AppRoutes.dismissLoader(context);
}
}
You need to call _getCategories after initState has completed.
#override
void initState() {
super.initState();
Future.delayed(Duration.zero, () {
this._getCategories();
});
// Could do this in one line: Future.delayed(Duration.zero, this._getCategories);
}
Also, you could do this on a different way, using addPostFrameCallback.
To make this task easier, you could create a mixin to be added to StatefulWidgets.
mixin PostFrameMixin<T extends StatefulWidget> on State<T> {
void postFrame(void Function() callback) =>
WidgetsBinding.instance?.addPostFrameCallback(
(_) {
// Execute callback if page is mounted
if (mounted) callback();
},
);
}
Then, you just need to plug this mixin to you page, like that:
class _MyPageState extends State<MyPage> with PostFrameMixin {
#override
void initState() {
super.initState();
postFrame(_getCategories);
}
}
Use the didChangeDependencies method which gets called after initState.
For your example:
#override
void initState() {
super.initState();
}
#override
void didChangeDependencies() {
super.didChangeDependencies();
this._getCategories();
}
void _getCategories() async {
// Omitted for brevity
// ...
}
Adding a frame callback might be better than using Future.delayed with a zero duration - it's more explicit and clear as to what is happening, and this kind of situation is what frame callback was designed for:
#override
void initState() {
super.initState();
WidgetsBinding.instance.addPostFrameCallback((_) async {
_getCategories();
});
}
an alternative is to put it inside PostFrameCallback which is between initState and Build.
#override
void initState() {
WidgetsBinding.instance.addPostFrameCallback((_) => getData());
super.initState();
}
getData() async {
}
There are many ways to solve this problem, override initState method:
#override
void initState() {
super.initState();
// Use any of the below code here.
}
Using SchedulerBinding mixin:
SchedulerBinding.instance!.addPostFrameCallback((_) {
// Call your function
});
Using Future class:
Future(() {
// Call your function
});
Using Timer class:
Timer(() {
// Call your function
});
The best solution i think is use the context from the Widget build. And paste the method _getCategories(context) after the build with the context from the tree.
So there is no problem with the widget tree.
When I click the raised button, the timepicker is showing up. Now, if I wait 5 seconds, for example, and then confirm the time, this error will occur:
setState() called after dispose()
I literally see in the console how flutter is updating the parent widgets, but why? I don't do anything - I just wait 5 seconds?!
The example below will work in a normal project, however in my project which is quite more complex it won't work because Flutter is updating the states while I am waiting... What am I doing wrong? Does anyone have a guess at what it could be that Flutter is updating randomly in my more complex project and not in a simple project?
[UPDATE]
I took a second look at it and found out it is updating from the level on where my TabBar and TabBarView are.
Could it have to do something with the "with TickerProviderStateMixin" which I need for the TabBarView? Could it be that it causes the app to refresh regularly and randomly?
class DateTimeButton extends State<DateTimeButtonWidget> {
DateTime selectedDate = new DateTime.now();
Future initTimePicker() async {
final TimeOfDay picked = await showTimePicker(
context: context,
initialTime: new TimeOfDay(hour: selectedDate.hour, minute: selectedDate.minute),
);
if (picked != null) {
setState(() {
selectedDate = new DateTime(selectedDate.year, selectedDate.month, selectedDate.day, picked.hour, picked.minute);
});
}
}
#override
Widget build(BuildContext context) {
return new RaisedButton(
child: new Text("${selectedDate.hour} ${selectedDate.minute}"),
onPressed: () {
initTimePicker();
}
);
}
}
Just check boolean property mounted of the state class of your widget before calling setState().
if (this.mounted) {
setState(() {
// Your state change code goes here
});
}
Or even more clean approach
Override setState method in your StatelfulWidget class.
class DateTimeButton extends StatefulWidget {
#override
void setState(fn) {
if(mounted) {
super.setState(fn);
}
}
}
If it is an expected behavior that the Future completes when the widget already got disposed you can use
if (mounted) {
setState(() {
selectedDate = new DateTime(selectedDate.year, selectedDate.month, selectedDate.day, picked.hour, picked.minute);
});
}
Just write one line before setState()
if (!mounted) return;
and then
setState(() {
//Your code
});
I had the same problem and i solved changing the super constructor call order on initState():
Wrong code:
#override
void initState() {
foo_bar(); // call setState();
super.initState(); // then foo_bar()
}
Right code:
#override
void initState() {
super.initState();
foo_bar(); // first call super constructor then foo_bar that contains setState() call
}
To prevent the error from occurring, one can make use of the mounted property of the State class to ensure that a widget is mounted before settings its state:
// First Update data
if (!mounted) {
return;
}
setState(() { }
Try this
Widget build(BuildContext context) {
return new RaisedButton(
child: new Text("${selectedDate.hour} ${selectedDate.minute}"),
onPressed: () async {
await initTimePicker();
}
);
}
class MountedState<T extends StatefulWidget> extends State<T> {
#override
Widget build(BuildContext context) {
return null;
}
#override
void setState(VoidCallback fn) {
if (mounted) {
super.setState(fn);
}
}
}
Example
To prevent the error,Instead of using State use MountedState
class ExampleStatefulWidget extends StatefulWidget {
const ExampleStatefulWidget({Key key}) : super(key: key);
#override
_ExampleStatefulWidgetState createState() => _ExampleStatefulWidgetState();
}
class _ExampleStatefulWidgetState extends MountedState<ExampleStatefulWidget> {
....
}
I had this error when I mistakenly called super.initState before the variable. Check this:
#override
void initState() {
super.initState();
bloc = MainBloc();
}
Should be fixed as
#override
void initState() {
bloc = MainBloc();
super.initState();
}
The problem could occur when you have long asynchronous operation in stateful widget that could be closed/disposed before the operation finished.
Futures in Dart are not preemptive, so the only way is to check if a widget mounted before calling setState.
If you have a lot of widgets with asynchrony, adding ton of if (mounted) checks is tedious and an extension method might be useful
extension FlutterStateExt<T extends StatefulWidget> on State<T> {
void setStateIfMounted(VoidCallback fn) {
if (mounted) {
// ignore: invalid_use_of_protected_member
setState(fn);
}
}
}