flutter - 如何从外部父小部件或另一个未来构建器访问未来构建器内部的功能
问题描述
我有一个填充列表视图的未来构建器，里面有一个函数 total() 计算，选择每个项目的价格总和并将其分配给小计变量。在底部，如果我分配小计变量，我将显示总价格，那么它将第一次返回 0，因为我的函数在未来的构建器中，我的意思是在分配值之后执行函数。所以我使用了另一个未来的构建器显示总金额，但我无法访问总函数，因为它在未来的构建器内部，并且它不能在类外部初始化，因为它有一些外部无法识别的数据。所以问题是我如何访问下面的总功能，我想到了全局键，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;
}
解决方案
尝试这个
@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,
),
),
);
}
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