Extract String From Future<String> In Flutter - flutter

Question

I'm using flutter, and I'm loading in a locally stored JSON file like so:
Future<String> loadJson(String file) async {
final jsonData = await rootBundle.loadString("path/to/$file.json");
return jsonData;
}
The problem is that this returns a Future<String> and I'm unable to extract the actual JSON data (as a String) from it.
I call loadJson in the Widget build method like so:
#override
Widget build(BuildContext context) {
final data = ModalRoute.of(context)!.settings.arguments as Map;
final file = data["file"];
String jsonData = loadJson(file); // The issue is here
return Scaffold (/* -- Snip -- */);
}
How would I go about doing this? Any help is appreciated.

Answer 1

loadJson is Future and you need to await for its result:
String jsonData = await loadJson(file);
you also can't run Future function inside build method, you need to use FutureBuilder:
return Scaffold (
body: FutureBuilder<String>(
future: loadJson(file),
builder: (context, snapshot) {
switch (snapshot.connectionState) {
case ConnectionState.waiting:
return Text('Loading....');
default:
if (snapshot.hasError) {
return Text('Error: ${snapshot.error}');
} else {
String jsonData = snapshot.data ?? "";
return /* -- Snip -- */;
},
}
}
},
),
);

Answer 2

You are getting data but not decoding it. You need to decode for using the loaded data.
Future<String> loadJson(String file) async {
final jsonData = await rootBundle.loadString("path/to/$file.json");
final data = await jsonDecode(jsonData)
return data;
}
Also, please don't forget to import dart convert library to use jsonDecode.
import 'dart:convert';