How to access the function inside a future builder from out side Parent widget or another future builder - flutter

Question

i have a future builder which populate a list view ,inside there is a function total() which calculate ,pick the price of each item sum it and assign it to the subtotal variable . on the bottom i am showing the total price if i assiggn subtotal variable then it will return 0 for the first time because my function is in future builder ,i mean the function is executed after the value is assign.so i used another future builder for showing the total amount but i cannot access the total function as it is inside the future builder and it cannot be initialzed outside in the class because it has some data that won't be recognized outside.
so the problem is how can i access total function below ,i thought of global key but i don't know how to use it.
import 'package:flutter/material.dart';
import 'package:restaurant_ui_kit/models/user.dart';
import 'package:restaurant_ui_kit/screens/checkout.dart';
import 'package:restaurant_ui_kit/util/database_helper.dart';
class CartScreen extends StatefulWidget {
#override
_CartScreenState createState() => _CartScreenState();
}
class _CartScreenState extends State<CartScreen>
with AutomaticKeepAliveClientMixin<CartScreen> {
var db = new DatabaseHelper();
int _subTotal = 0;
List _users = [];
#override
Widget build(BuildContext context) {
super.build(context);
return Scaffold(
body: Padding(
padding: EdgeInsets.fromLTRB(10.0, 0, 10.0, 0),
child: FutureBuilder<List>(
future: db.getAllUsers(),
initialData: List(),
builder: (context, snapshot) {
return snapshot.hasData
? ListView.builder(
itemCount: snapshot.data.length,
itemBuilder: (context, position) {
final item = snapshot.data[position];
total(){
for (int i = 0; i < snapshot.data.length; i++) {
if (i == 0){
_subTotal =0;
}
_subTotal = _subTotal +
int.parse(
User.fromMap(snapshot.data[position]).price);
}
return _subTotal;
}
total();
// print('toatl is $_subTotal');
// get your item data here ...
return Dismissible(
key: UniqueKey(),
child: new Card(
color: Colors.white,
elevation: 2.0,
child: new ListTile(
leading: new CircleAvatar(
child: Text(
"${User.fromMap(snapshot.data[position]).name.substring(0, 1)}"),
),
title: new Text(
"User: ${User.fromMap(snapshot.data[position]).price}"),
subtitle: new Text(
"Id: ${User.fromMap(snapshot.data[position]).id}"),
onTap: () => debugPrint(
"${User.fromMap(snapshot.data[position]).id}"),
),
),
background: slideLeftBackground(),
confirmDismiss: (direction) async {
if (direction == DismissDirection.endToStart) {
final bool res = await showDialog(
context: context,
builder: (BuildContext context) {
return AlertDialog(
content: Text(
"Are you sure you want to delete ${User.fromMap(snapshot.data[position]).name}?"),
actions: <Widget>[
FlatButton(
child: Text(
"Cancel",
style: TextStyle(color: Colors.black),
),
onPressed: () {
Navigator.of(context).pop();
},
),
FlatButton(
child: Text(
"Delete",
style: TextStyle(color: Colors.red),
),
onPressed: () {
// TODO: Delete the item from DB etc..
setState(() {
// total();
// print(position);
print('toatl is $_subTotal');
if (position == 0) {
//print('index 0 dai');
db.deleteUser(User.fromMap(
snapshot.data[position])
.id);
_subTotal = 0;
// print('toatl is 0 $_subTotal');
//snapshot.data.removeAt(position);
} else {
snapshot.data
.removeAt(--position);
db.deleteUser(User.fromMap(
snapshot.data[position])
.id);
total();
// print('toatl sewa $_subTotal');
}
//print("removed");
// print('mSubTotal $mSubTotal');
});
Navigator.of(context).pop();
},
),
],
);
});
return res;
}
},
);
},
)
: Center(
child: CircularProgressIndicator(),
);
},
),
),
floatingActionButton: FloatingActionButton(
tooltip: "Checkout",
onPressed: () {
Navigator.of(context).push(
MaterialPageRoute(
builder: (BuildContext context) {
return Checkout();
},
),
);
},
child: Icon(
Icons.arrow_forward,
),
heroTag: Object(),
),
bottomSheet: Card(
elevation: 4.0,
child: Container(
child: ListView(
physics: NeverScrollableScrollPhysics(),
children: <Widget>[
SizedBox(height: 10.0),
Row(
mainAxisAlignment: MainAxisAlignment.spaceBetween,
children: <Widget>[
Padding(
padding: EdgeInsets.fromLTRB(10,5,5,5),
child: Column(
crossAxisAlignment: CrossAxisAlignment.start,
children: <Widget>[
Text(
"Total",
style: TextStyle(
fontSize: 13,
fontWeight: FontWeight.w400,
),
),
FutureBuilder(
**future: total(),** the problem is here it cannot be accessed
builder: (BuildContext context, AsyncSnapshot snapshot) {
if(snapshot.hasData){
return Text(
snapshot.data.toString(),
style: TextStyle(
color: Colors.white,
fontSize: 8,
),
textAlign: TextAlign.center,
);
}
return Container();
}
),
Text(
"Delivery charges included",
style: TextStyle(
fontSize: 11,
fontWeight: FontWeight.w400,
),
),
],
),
),
Container(
padding: EdgeInsets.fromLTRB(5,5,10,5),
width: 150.0,
height: 50.0,
child: FlatButton(
color: Theme.of(context).accentColor,
child: Text(
"Place Order".toUpperCase(),
style: TextStyle(
color: Colors.white,
),
),
onPressed: (){},
),
),
],
),
],
),
height: 70,
),
),
);
}
#override
bool get wantKeepAlive => true;
}

Answer 1

Well first off you can take out your total function and just pass in the data argument once it becomes available in the futurebuilder(like total(data){...}).
Now if you need the data that you got from db.getAllUsers(), you could also create a function like getAllUsers, where you would assign the gotten value to a class variable to be used later. Finally, unless the function total is asynchronous, it does not make sense to have a future builder for it. You can probably get away with calling setState once the total value is available.

Answer 2

Try this
#override
Widget build(BuildContext context) {
super.build(context);
return Scaffold(
body: Padding(
padding: EdgeInsets.fromLTRB(10.0, 0, 10.0, 0),
child: FutureBuilder<List>(
future: db.getAllUsers(),
initialData: List(),
builder: (context, snapshot) {
total() {
num subTotal = 0;
for (int i = 0; i < snapshot.data.length; i++) {
subTotal += int.parse(User.fromMap(snapshot.data[i]).price);
}
setState(() {
_subTotal=subTotal;
});
}
if (snapshot.hasData) {
ListView.builder(
itemCount: snapshot.data.length,
itemBuilder: (context, position) {
final item = snapshot.data[position];
total();
// print('toatl is $_subTotal');
// get your item data here ...
return Dismissible(
key: UniqueKey(),
child: new Card(
color: Colors.white,
elevation: 2.0,
child: new ListTile(
leading: new CircleAvatar(
child: Text(
"${User.fromMap(snapshot.data[position]).name.substring(0, 1)}"),
),
title: new Text(
"User: ${User.fromMap(snapshot.data[position]).price}"),
subtitle: new Text(
"Id: ${User.fromMap(snapshot.data[position]).id}"),
onTap: () => debugPrint(
"${User.fromMap(snapshot.data[position]).id}"),
),
),
background: slideLeftBackground(),
confirmDismiss: (direction) async {
if (direction == DismissDirection.endToStart) {
final bool res = await showDialog(
context: context,
builder: (BuildContext context) {
return AlertDialog(
content: Text(
"Are you sure you want to delete ${User.fromMap(snapshot.data[position]).name}?"),
actions: <Widget>[
FlatButton(
child: Text(
"Cancel",
style: TextStyle(color: Colors.black),
),
onPressed: () {
Navigator.of(context).pop();
},
),
FlatButton(
child: Text(
"Delete",
style: TextStyle(color: Colors.red),
),
onPressed: () {
// TODO: Delete the item from DB etc..
setState(() {
// total();
// print(position);
print('toatl is $_subTotal');
if (position == 0) {
//print('index 0 dai');
db.deleteUser(User.fromMap(
snapshot.data[position])
.id);
_subTotal = 0;
// print('toatl is 0 $_subTotal');
//snapshot.data.removeAt(position);
} else {
snapshot.data.removeAt(--position);
db.deleteUser(User.fromMap(
snapshot.data[position])
.id);
total();
// print('toatl sewa $_subTotal');
}
//print("removed");
// print('mSubTotal $mSubTotal');
});
Navigator.of(context).pop();
},
),
],
);
});
return res;
}
return null;
},
);
},
);
}
return Center(child: CircularProgressIndicator());
},
),
),
floatingActionButton: FloatingActionButton(
tooltip: "Checkout",
onPressed: () {
Navigator.of(context).push(
MaterialPageRoute(
builder: (BuildContext context) {
return Checkout();
},
),
);
},
child: Icon(
Icons.arrow_forward,
),
heroTag: Object(),
),
bottomSheet: Card(
elevation: 4.0,
child: Container(
child: ListView(
physics: NeverScrollableScrollPhysics(),
children: <Widget>[
SizedBox(height: 10.0),
Row(
mainAxisAlignment: MainAxisAlignment.spaceBetween,
children: <Widget>[
Padding(
padding: EdgeInsets.fromLTRB(10, 5, 5, 5),
child: Column(
crossAxisAlignment: CrossAxisAlignment.start,
children: <Widget>[
Text(
"Total",
style: TextStyle(
fontSize: 13,
fontWeight: FontWeight.w400,
),
),
// changes
Text(
_subTotal.toString(),
style: TextStyle(
color: Colors.white,
fontSize: 8,
),
textAlign: TextAlign.center,
),
Text(
"Delivery charges included",
style: TextStyle(
fontSize: 11,
fontWeight: FontWeight.w400,
),
),
],
),
),
Container(
padding: EdgeInsets.fromLTRB(5, 5, 10, 5),
width: 150.0,
height: 50.0,
child: FlatButton(
color: Theme.of(context).accentColor,
child: Text(
"Place Order".toUpperCase(),
style: TextStyle(
color: Colors.white,
),
),
onPressed: () {},
),
),
],
),
],
),
height: 70,
),
),
);
}