How to refresh a widget with stream builder in flutter

Question

I am trying to show data from the text file as per the data stored in shared preference i have another screen to save data in the text file i have a stream builder earlier it was future builder So i am trying to refresh the screen when coming back from second screen i tried to call a method when pop the method is getting called in the viewmodel calss of provider but the streambuilder is not getting updated this is the code

to fetch data

Future<List<String>> fetchdata() async {
SharedPreferences prefs = await SharedPreferences.getInstance();
String? category = prefs.getString('category');
if (category != null) {
  lines = await locator<JsonAPI>().fetchquotes(category);
} else {
  lines = await locator<JsonAPI>().fetchquotes('quotes');
}
// data = lines as Future<List<String>>;
notifyListeners();
return lines;
}

stream builder

         var quotesdata = Provider.of<HomeViewModel>(context, listen: false);

 StreamBuilder(
              stream: quotesdata.fetchdata().asStream(),
              builder: (context, AsyncSnapshot snapshot) {
                if (snapshot.hasData) {
                  List<String> lines = quotesdata.lines;
                  // List<String>? lines = snapshot.data as List<String>?;
                  return ScreenShotWidget(
                    homeViewModel: quotesdata,
                    list: lines,
                  );
                } else {
                  return Container();
                }
              }),

method that i call when pop

function(data) {
category = data.toString();
fetchdata();
notifyListeners();
setState() {}
}

any idea how to update the screen

Could you specify what quotesdata is and where it is created? — Lulupointu, Sep 28 '21 at 08:40

score 1 · Accepted Answer · answered Sep 28 '21 at 08:51

1

Every time your widget rebuilds, you get a new stream. This is a mistake. You should obtain the stream only once (for example, in initState)

@override
void initState() {
  _stream = quotesdata.fetchdata().asStream();
}

and use that stream variable with StreamBuilder

 StreamBuilder(
   stream: _stream,

Later, when you want to update the stream, you can do

setState(() {
  _stream = quotesdata.fetchdata().asStream();
})

to change the stream and force a refresh.

Please go over your code and change all such usages

 StreamBuilder(
   stream: quotesdata.fetchdata().asStream(),

to this kind of usage.

 StreamBuilder(
   stream: _stream,

Otherwise you may get a high backend bill someday. Right now every screen refresh does a new query to the backend.

answered Sep 28 '21 at 08:51

Gazihan Alankus

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but quotesdata is a provider object how i can use it prior initializing?? – Neelay Srivastava Sep 28 '21 at 12:34
there are some ways here: https://stackoverflow.com/questions/60343605/how-to-use-data-from-provider-during-initstate-in-flutter-application an alternative is for parent to get it and pass it to constructor of this widget. – Gazihan Alankus Sep 28 '21 at 13:43
You just CANNOT call fetchdata() within your build function. – Gazihan Alankus Sep 28 '21 at 16:16
hey just a question when i pop the second screen does this method suppose to auto refresh ? a i have to setstate method in the function – Neelay Srivastava Sep 29 '21 at 00:02
you mean after you show this screen with the stream, you show a second screen and when you come back to this you want this to refresh? – Gazihan Alankus Sep 29 '21 at 06:07
Yes you have to do setstate. You can do this: – Gazihan Alankus Sep 29 '21 at 06:07
```await Navigator.push(...); setState(...)``` – Gazihan Alankus Sep 29 '21 at 06:07

How to refresh a widget with stream builder in flutter

1 Answers1