void initState() {
super.initState();
showAlertDialog(context);
i want to show alertdialog in state
I've tried the following methods but it doesn't work
can you tell me what to do!
You can do by using 'addPostFrameCallback' method.
https://api.flutter.dev/flutter/scheduler/SchedulerBinding/addPostFrameCallback.html
void initState() {
super.initState();
WidgetsBinding.instance
.addPostFrameCallback((_) => showAlertDialog(context));
}
Related
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();
Hi IM trying to load initial data from db and sharepref as user first open page.
...
List questionsList = [];
bool _languageA = false;
#override
void initState() {
super.initState();
loadData(); // seting for some dropdown menu
_getLanguageChoise(); //geting from sharepref bool value
_getData(arabic: _languageArabic).then((value) { //async db call load List ext...
setState(() {});
});
}
Problem is that "questionsList" and "_languageA" bool is not filed in initState , so I get null or initial value, only when I refresh state or reload
List get filed and var get value... So what I need to do in order to have initial filed variables before build method so user can see..
assign questionsList and _languageA values inside initState method just like this in order to initialize a field value when the widget is created
void initState() {
super.initState();
questionsList=["hello"];
_languageA=true;
}
Make your initstate like this
#override
void initState() {
super.initState();
questionsList=[""];
_languageA=true;
loadData(); // seting for some dropdown menu
_getLanguageChoise(); //geting from sharepref bool value
_getData(arabic: _languageArabic).then((value) { //async db call load List ext...
setState(() {});
});
}
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 create a button to test the database. it returns a set of data. While i did in initState function, what i get is null.
#override
void initState() {
db.queryData('username').then((val) {
_userAuthData = val;
});
super.initState();
print(_userAuthData);
}```
** both async/await and future.then() works the same in button on press function.
you can execute async function on init method by using future
#override
void initState() {
super.initState();
Future.delayed(Duration.zero,()async{
final _userAuthData=await db.queryData('username');
print(_userAuthData);
});
});
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.