在 API 中使用用户输入以按用户加载数据时发现预期
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【中文标题】在 API 中使用用户输入以按用户加载数据时发现预期【英文标题】：Expection found while using user input in an API to load data as per user 【发布时间】：2020-11-07 04:33:21 【问题描述】：我试图从 ListView Builder 中的 API 接收数据，使用用户输入来显示要显示的票证数量。 这是我试图反映用户输入的地方。 每次我在列表视图构建器之前使用文本字段时，我都会收到错误
import 'package:flutter/material.dart';
import 'package:http/http.dart' as http;
import 'dart:convert';
class Ticket
Ticket(
this.tickets,
);
List<List<List<int>>> tickets;
factory Ticket.fromJson(Map<String, dynamic> json) => Ticket(
tickets: List<List<List<int>>>.from(json["tickets"].map((x) =>
List<List<int>>.from(
x.map((x) => List<int>.from(x.map((x) => x)))))),
);
Map<String, dynamic> toJson() =>
"tickets": List<dynamic>.from(tickets.map((x) => List<dynamic>.from(
x.map((x) => List<dynamic>.from(x.map((x) => x)))))),
;
class TicketPage extends StatefulWidget
@override
_TicketPageState createState() => _TicketPageState();
class _TicketPageState extends State<TicketPage>
String _nos = '0';
Ticket ticketList;
String apiResult;
Map<String, bool> cellStatus = ;
final numCon = TextEditingController();
@override
void initState()
super.initState();
_getNumbers();
numCon.addListener(_updateUserInput);
_updateUserInput()
_nos = numCon.text;
@override
void dispose()
// Clean up the controller when the widget is removed from the widget tree.
// This also removes the listener.
numCon.dispose();
super.dispose();
_getNumbers() async
var result = await http
.post(
'https://tickets-qzd55332wa-de.a.run.app/generateTickets?ticketsRequired=$_nos')
.then((result)
//Waits for the API response and assigns to apiResult variable
setState(()
apiResult = result.body;
);
);
// List tick = [
//
// 'tickets': [
// [
// [11, 5, 7, 10, 28, 9, 7, 74, 59],
// [1, 15, 7, 10, 8, 79, 27, 74, 9],
// [71, 5, 7, 20, 18, 9, 77, 74, 79],
// ],
// [
// [21, 5, 7, 80, 8, 9, 7, 74, 49],
// [31, 15, 7, 10, 18, 79, 7, 74, 19],
// [71, 5, 7, 20, 18, 79, 77, 74, 29],
// ],
// ]
// ,
// ];
@override
Widget build(BuildContext context)
var h = MediaQuery.of(context).size.height;
var w = MediaQuery.of(context).size.width;
if (apiResult == null)
return Scaffold(body: Center(child: CircularProgressIndicator()));
else
//Get an instance of Ticket from the API assigned to apiResponse variable
ticketList = Ticket.fromJson(json.decode(apiResult));
print('Tickets: $ticketList.tickets');
return Scaffold(
body: SafeArea(
child: Column(
children: <Widget>[
Padding(
padding: const EdgeInsets.all(28.0),
child: Container(
child: TextField(
controller: numCon,
decoration: InputDecoration(
hintText: 'nos',
),
),
),
),
RaisedButton(onPressed: ()
setState(()
_getNumbers();
);
),
Center(
child: Padding(
padding: const EdgeInsets.all(20.0),
child: Container(
decoration: BoxDecoration(
border: Border.all(
color: Colors.black,
)),
child: ListView.builder(
itemCount: ticketList.tickets.length,
itemBuilder: (BuildContext context, index)
List tripleNumbersList = [];
List<Widget> cells = [];
List<Widget> rows = [];
//Get the lists of lists inside the 'tickets' list
tripleNumbersList = ticketList.tickets[index];
//Iterates over each list with other 3 lists
for (int j = 0; j < tripleNumbersList.length; j++)
//Get one of the 3 lists
List<int> list = tripleNumbersList[j];
//Iterates over the list of numbers
for (int k = 0; k < list.length; k++)
//Adds a Widget to 'cells; list for each number
cells.add(Container(
height: 40,
width: 40,
decoration: BoxDecoration(
border: Border.all(
color: Colors.black,
),
//color: Colors.pink
),
child: GestureDetector(
onTap: ()
print('Working');
if (cellStatus['$j$k'] ?? true)
print('Working');
setState(()
cellStatus.addAll('$j$k': false);
);
,
child: list[k] != 0
? Text(
' $list[k] ',
style: TextStyle(
fontSize: 18.0,
fontWeight: FontWeight.bold),
)
: Text(''),
)));
//Adds the list of 'cells' in the 'rows' list
rows.add(Row(children: cells));
cells = [];
//Adds a empty row to make space
rows.add(Row(children: [
Container(
height: 10,
)
]));
return Center(
child: Container(
height: h / 5,
decoration: BoxDecoration(
border: Border.all(
color: Colors.black,
),
//color: Colors.pink
),
child: Column(
//Adds the list of rows to the column
children: rows,
),
),
);
,
),
),
),
),
],
),
),
);
它正在抛出异常
RenderBox was not laid out: RenderCustomPaint#aecb2 relayoutBoundary=up8 NEEDS-PAINT NEEDS-COMPOSITING-BITS-UPDATE
'package:flutter/src/rendering/box.dart':
Failed assertion: line 1694 pos 12: 'hasSize'
The relevant error-causing widget was
ListView
RenderBox was not laid out: RenderPadding#d9b88 relayoutBoundary=up1 NEEDS-PAINT NEEDS-COMPOSITING-BITS-UPDATE
'package:flutter/src/rendering/box.dart':
Failed assertion: line 1694 pos 12: 'hasSize'
The relevant error-causing widget was
Scaffold
我希望我能解释这个问题，并希望看到帮助我解决这个问题。 我一直被这个问题困扰。
【问题讨论】：
请看@JideGuru 我确实经历了所有这些例子，现在我坚持这个....尝试使用文本控制器仍然弹出错误。这就是为什么我正在寻找这个问题的帮助@dev-aentgs 这一篇更好地涵盖了这些步骤：Handle changes to a text field。你能用TextEditingController 发布更新的代码吗？
我已经做出了改变...请看@dev-aentgs
【参考方案1】：
由于ListView 嵌套在Column 中而发生错误。
上面的代码可以修改为将ListView包裹在Expanded中。参考this answer
例子：
@override
Widget build(BuildContext context)
return _buildList(context);
Widget _buildList(BuildContext context)
var h = MediaQuery.of(context).size.height;
if (apiResult == null)
return Scaffold(body: Center(child: CircularProgressIndicator()));
else
//Get an instance of Ticket from the API assigned to apiResponse variable
ticketList = Ticket.fromJson(json.decode(apiResult));
print('$ticketList.tickets.length Tickets: $ticketList.tickets');
return SafeArea(
child: Scaffold(
appBar: AppBar(
title: Text('SO 62967820'),
),
body: Column(
children: [
Padding(
padding: const EdgeInsets.all(28.0),
child: Container(
child: TextField(
controller: numCon,
decoration: InputDecoration(
hintText: 'nos',
),
),
),
),
RaisedButton(
child: Text('Generate'),
onPressed: ()
setState(()
_getNumbers();
);
),
Expanded(
child: ListView.builder(
itemCount: ticketList.tickets.length,
itemBuilder: (BuildContext context, index)
List tripleNumbersList = [];
List<Widget> cells = [];
List<Widget> rows = [];
//Get the lists of lists inside the 'tickets' list
tripleNumbersList = ticketList.tickets[index];
//Iterates over each list with other 3 lists
for (int j = 0; j < tripleNumbersList.length; j++)
//Get one of the 3 lists
List<int> list = tripleNumbersList[j];
//Iterates over the list of numbers
for (int k = 0; k < list.length; k++)
//Adds a Widget to 'cells; list for each number
cells.add(Container(
height: 40,
width: 40,
decoration: BoxDecoration(
border: Border.all(
color: Colors.black,
),
//color: Colors.pink
),
child: GestureDetector(
onTap: ()
print('Working');
if (cellStatus['$j$k'] ?? true)
print('Working');
setState(()
cellStatus.addAll('$j$k': false);
);
,
child: list[k] != 0
? Text(
' $list[k] ',
style: TextStyle(
fontSize: 18.0,
fontWeight: FontWeight.bold),
)
: Text(''),
)));
//Adds the list of 'cells' in the 'rows' list
rows.add(Row(children: cells));
cells = [];
//Adds a empty row to make space
rows.add(Row(children: [
Container(
height: 10,
)
]));
return Center(
child: Container(
height: h / 5,
decoration: BoxDecoration(
border: Border.all(
color: Colors.black,
),
//color: Colors.pink
),
child: Column(
//Adds the list of rows to the column
children: rows,
),
),
);
,
),
),
],
),
),
);
【讨论】：
但是那个扩展的小部件起了什么作用 不完全确定，但根据我对错误的理解和this answer 的解释，Expanded 小部件负责为父级Column 中的ListView 分配适当的高度。 @PratyaySinha
嘿！如果您能看看我面临的这个问题，将不胜感激***.com/questions/68603763/…以上是关于在 API 中使用用户输入以按用户加载数据时发现预期的主要内容，如果未能解决你的问题，请参考以下文章