How to pass parameters into the future instance of Futurebuilder? - flutter

Question

I am trying to pass parameters into the future instance but I encounter the "error instance member can't be accessed in an initializer" for _getData at future: _getData even though I have initialized it in initState.
class _DisplayListState extends State<DisplayList> {
late Future<QuerySnapshot> _getData;
Future<QuerySnapshot> getData(String value)async{
return await FirebaseFirestore.instance
.collection('x')
.where('a', isEqualTo: value)
.get();
}
#override
void initState(){
super.initState();
_getData = getData(widget.value);
}
Widget displayList = FutureBuilder(
future: _getData,
builder: (BuildContext context, AsyncSnapshot<QuerySnapshot> snapshot) {
return Container();
},
);
#override
Widget build(BuildContext context) {
return Scaffold(
body: displayList,
);
}
}
I remove the the parameters for getData thinking that I should simplify the problem first and tried future: getData() but I encoutered the same error.
The only way that I don't encounter the error is if I do this - future: FirebaseFirestore.instance.collection('x').where('a', isEqualTo: 'something').get() for FutureBuilder. But this means I cannot pass parameters and I would prefer to use a function/variable for this over the long line of code.
future: FirebaseFirestore.instance.collection('x').where('a', isEqualTo: value).get() where value=widget.value is initialized in initState will give me the same error.

Answer 1

You can use a method for displayList instead of a variable.
You can change this:
Widget displayList = FutureBuilder(
future: _getData,
builder: (BuildContext context, AsyncSnapshot<QuerySnapshot> snapshot) {
return Container();
},
);
to this:
Widget getDisplayList() => FutureBuilder(
future: _getData,
builder: (BuildContext context, AsyncSnapshot<QuerySnapshot> snapshot) {
return Container();
},
);
And in the Scaffold's body, use the method like this:
body: getDisplayList()