I check some similar topics regarding this, but couldn’t find a solution to my problem.
I created a FutureBuilder on my Home screen, because I want to use the result of an asynchronous function (that reads a JSON) to build it. I’m calling this async function in the FutureBuilder’s "future:", but apparently the program is continuing to build the screen before receiving the data from the "future" (which is coming up empty).
I debugged the function, and it retrieves the desired JSON data, but apparently it is not giving enough time to return to the FutureBuilder, because when I see the "snapshot.data", it is empty.
Is this the case? Doesn’t FutureBuilder expect the result from "future:"? What to do then?
Here is my Home screen with the FutureBuilder:
class _HomePageState extends State<HomePage> {
@override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: const Text("Country Population Guesser"),
),
backgroundColor: ThemeColors.primaryColor[900],
**body: FutureBuilder<List<Country>>(
future: CountryDAO().fetchJSON()**,
builder: (context, snapshot) {
List<Country>? countryList = snapshot.data;
if (snapshot.connectionState != ConnectionState.done) {
return Center(
child: Column(
children: [
CircularProgressIndicator(),
Text('Loading'),
],
),
);
}
//print("${snapshot.hasData} + ${countryList}");
if (snapshot.hasData && countryList != null) {
if (countryList.isNotEmpty) {
...
And here’s the function I’m calling:
class CountryDAO {
**Future<List<Country>> fetchJSON() async** {
final String response = await rootBundle.loadString('assets/database.json');
final data = json.decode(response);
final List<Country> countryList = convertToList(data["countries"]);
return countryList;
}
List<Country> convertToList(List<Map<String, dynamic>> countryMap){
List<Country> countryList = [];
for(var country in countryMap){
print(country);
countryList.add(Country.fromMap(country));
}
return countryList;
}
}
UPDATE: The problem was not the FutureBuilder, but the function creating a wrong type cast and was crashing without a proper error message.
Thanks!
2
Answers
countryList
should be assigned value only after snapshot has data.try to follow this official example : https://api.flutter.dev/flutter/widgets/FutureBuilder-class.html