Flutter : The onRefresh callback returned null - flutter

Question

Sorry I'm new to flutter and trying to learn it. I have an issue with RefreshIndicator.
When I try pulling it I got an error like below :
════════ Exception caught by material library ══════════════════════════════════════════════════════
The following assertion was thrown when calling onRefresh:
The onRefresh callback returned null.
The RefreshIndicator onRefresh callback must return a Future.
════════════════════════════════════════════════════════════════════════════════════════════════════
Currently I am using flutter_bloc. Here is my sample code
TableList_bloc.dart
import 'dart:async';
import 'package:bloc/bloc.dart';
import 'package:http/http.dart' as http;
import 'dart:convert';
import 'package:pos_project_bloc/modal/api.dart';
class ModalTableList {
final String Table_Number;
final String Name_Table;
ModalTableList(
this.Table_Number,
this.Name_Table,
);
}
class tablelistbloc extends Bloc<bool, List<ModalTableList>>{
#override
// TODO: implement initialState
List<ModalTableList> get initialState => [];
#override
Stream<List<ModalTableList>> mapEventToState(bool event) async* {
// TODO: implement mapEventToState
List<ModalTableList> tablelist =[];
try {
final response = await http.get(BaseUrl.GetTableList);
final data = jsonDecode(response.body);
if (data.length != 0) {
data.forEach((api) {
tablelist.add(
ModalTableList(
api['Table_Number'],
api['Name_Table'],
)
);
print("test"+api['Table_Number'].toString());
});
print("Get Table List : sukses");
} else {
print('data kosong');
}
} catch (e) {
print("Error GetTableList :");
print(e);
}
yield tablelist;
}
}
TabeList.dart
import 'package:flutter/material.dart';
import 'package:flutter_bloc/flutter_bloc.dart';
import 'package:pos_project_bloc/bloc/TableList_bloc.dart';
import 'package:pos_project_bloc/modal/SharedPreferences.dart';
class TableList extends StatefulWidget {
#override
_TableListState createState() => _TableListState();
}
class _TableListState extends State<TableList> {
#override
void initState() {
super.initState();
BlocProvider.of<tablelistbloc>(context).add(true);
}
Widget build(BuildContext context) {
final GlobalKey<RefreshIndicatorState> refresh = GlobalKey<RefreshIndicatorState>();
Future<Null> _refresh() async{
BlocProvider.of<tablelistbloc>(context).add(true);
}
return Scaffold(
appBar: AppBar(
backgroundColor: Colors.lightBlueAccent,
title: new Center(
child: new Text('Available Table',
style: new TextStyle(color: Colors.white, fontSize: 15.0)),
)
),
floatingActionButton: Container(
child: Column(
mainAxisAlignment: MainAxisAlignment.end,
children: <Widget>[
Padding(
padding: EdgeInsets.all(5.0),
child: FloatingActionButton.extended(
heroTag: 1,
icon: Icon(Icons.refresh),
label: Text('Refresh Table List'),
onPressed: () {
BlocProvider.of<tablelistbloc>(context).add(true);
},
),
)
],
),
),
body: RefreshIndicator(
onRefresh: (){
_refresh();
},
key: refresh,
child: BlocBuilder<tablelistbloc,List<ModalTableList>>(
builder: (context,tablelist)=> ListView.builder(
itemCount: tablelist.length,
itemBuilder: (context,index){
final x = tablelist[index];
return GestureDetector(
onTap: (){
print("Selected Available Table On Tap : " + x.Table_Number);
Shared_Preferences().SaveTableNumber(
x.Table_Number
);
Navigator.pushReplacementNamed(context, '/POS');
},
child: Container(
decoration: BoxDecoration(
border: Border(
bottom: BorderSide(
width: 2.0,
color: Colors.grey.withOpacity(0.4),
))),
padding: EdgeInsets.all(10.0),
child: Row(
children: <Widget>[
Icon(
Icons.table_chart,
size: 100.0,
color: Colors.lightBlueAccent,
),
Column(
crossAxisAlignment: CrossAxisAlignment.start,
children: <Widget>[
Text(
'Table Number : ' + x.Table_Number,
style: TextStyle(
fontSize: 20.0,
fontWeight: FontWeight.bold,
color: Colors.lightBlueAccent),
),
Text(
'Name : ' + x.Name_Table,
style: TextStyle(
fontSize: 20.0,
fontWeight: FontWeight.bold,
color: Colors.lightBlueAccent),
),
],
)
],
),
),
);
},
),
),
)
);
}
}

Answer 1

Just add async.
onRefresh: () async {
GetTableList.add(true);
},
onRefresh is a RefreshCallback, and RefreshCallback is a Future Function().
So if GetTableList.add(true) not return Future, must to add async.

Answer 2

it is says onRefresh callback must return a Future.
and it is seems like your are not returning Future from onRefresh
onRefresh: _refresh
Future<Null> _refresh() async{
GetTableList.add(true);
}
hope it helps..

Answer 3

You can problably use the following:
Future<bool> refresh() async {
//your refresh code
return true;
}