我有一个将来的构建器，它会填充一个列表视图，里面有一个函数total（）来计算，选择每个项目的价格，将其总和并将其分配给小计变量。在底部，我显示的是总价格，如果我将小计变量设置为小计，则它将首次返回0，因为我的函数位于“将来的构建器”中，这意味着该函数将在赋值后执行。所以我使用了另一个“将来的构建器”显示总金额，但我无法访问总功能，因为它位于将来的构建器内部，并且无法在类的外部初始化，因为它具有一些外部无法识别的数据。 所以问题是我该如何访问下面的全部功能，想到了全局键，但我不知道如何使用它。
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;
}
答案 0 :(得分：0)
首先，您可以取出total函数，并在data参数在futurebuilder中可用后再传递它（例如total（data）{...}）。
现在，如果您需要从db.getAllUsers（）获得的数据，则还可以创建一个类似getAllUsers的函数，在该函数中，将获得的值分配给一个类变量，以供以后使用。最后，除非函数total是异步的，否则没有必要为其提供将来的构建器。一旦总值可用，您就可以调用setState逃脱。
答案 1 :(得分：0)
尝试一下
@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,
),
),
);
}