【发布时间】：2021-03-06 22:32:23
【问题描述】：
我正在尝试构建一个抽屉，从文件中的 json 获取它的项目。当我在调试时进行此操作时，我可以看到它加载了项目，但我的最后一个抽屉导致错误。它指出
[VERBOSE-2:ui_dart_state.cc(186)] 未处理的异常：类型 “List”不是“Map
”类型的子类型 #0 loadDropDowns (package:carded1/main.dart:31:36)
为了完成这项工作，
- 创建资产文件夹
- 将此添加到 pubspec.yaml：
资产：
- assets/jsonfile.json
-
将此添加到 jsonfile.json
[{ “标题”：“保险”， “listOfItems”：[“亨利”、“杰瑞”、“乱舞”] }, { “标题”：“保险”， “listOfItems”：[“亨利”、“杰瑞”、“乱舞”] }, { “标题”：“保险”， “listOfItems”：[“亨利”、“杰瑞”、“乱舞”] } ]
这是我的 main.dart 文件：
import 'package:flutter/material.dart';
import 'package:flip_card/flip_card.dart';
import 'dart:convert';
import 'dart:async' show Future;
import 'package:flutter/services.dart' show rootBundle;
// String rawJson = '{"header":"Insurance","listOfItems":["henry","jerry","flurry"]}';
// Map<String, dynamic> map = jsonDecode(rawJson);
// String header = map['header'];
// List<dynamic> listOfItems = map['listOfItems'];
//List<ExpansionTile> listOfTilesToBuild = [];
void main() {
runApp(FlipCarded());
}
Future wait(int seconds) {
return new Future.delayed(Duration(seconds: seconds), () => {});
}
Future<String> _loadADropDownListAsset() async {
return await rootBundle.loadString('assets/jsonfile.json');
}
Future<DropDownItem> loadDropDowns() async {
await wait(5);
String jsonString = await _loadADropDownListAsset();
final jsonResponse = json.decode(jsonString);
return new DropDownItem.fromJson(jsonResponse);
}
class FlipCarded extends StatelessWidget {
@override
Widget build(BuildContext context) {
return MaterialApp(
title: 'FlipCard',
theme: ThemeData.dark(),
home: HomePage(),
);
}
}
class DropDownItem{
DropDownItem({this.header, this.listOfItems});
final String header;
final List<String> listOfItems;
factory DropDownItem.fromJson(Map<String, dynamic> json){
return DropDownItem(
header: json['header'],
listOfItems: List<String>.from(json['listOfItems'].map((x) => x)),
);
}
Map<String, dynamic> toJson() {
return {
'header': header,
'listOfItems': listOfItems,
};
}
}
class HomePage extends StatelessWidget {
Widget futureDropdown(){
return new FutureBuilder<DropDownItem>(
future: loadDropDowns(),
builder: (context, snapshot) {
if (snapshot.hasData) {
return new ExpansionListTile(header: snapshot.data.header, listOfItems: snapshot.data.listOfItems);
} else if (snapshot.hasError) {
return new ExpansionTile(title: Text('Error'));
}
return new CircularProgressIndicator();
}
);
}
//DropDownItem dItem = DropDownItem(header: header, listOfItems: listOfItems);
_renderBg() {
return Container(
decoration: BoxDecoration(color: const Color(0xFFFFFFFF)),
);
}
_renderAppBar(context) {
return MediaQuery.removePadding(
context: context,
removeBottom: true,
child: AppBar(
brightness: Brightness.dark,
elevation: 0.0,
backgroundColor: Color(0xFFFFFFFF),
),
);
}
_renderContext(context) {
return Card(
elevation: 0.0,
margin:
EdgeInsets.only(left: 32.0, right: 32.0, top: 20.0, bottom: 0.0),
color: Color(0x00000000),
child: FlipCard(
direction: FlipDirection.VERTICAL,
speed: 1000,
onFlipDone: (status) {
print(status);
},
front: Container(
decoration: BoxDecoration(
color: Color(0xFF006666),
borderRadius: BorderRadius.all(Radius.circular(8.0)),
),
child: Column(
mainAxisAlignment: MainAxisAlignment.center,
children: <Widget>[
Text(
'Back',
style: Theme.of(context).textTheme.headline1,
),
Text('Click here to flip front',
style: Theme.of(context).textTheme.bodyText1),
],
),
),
back: Container(
decoration: BoxDecoration(
color: Color(0xFF006666),
borderRadius: BorderRadius.all(Radius.circular(8.0)),
),
child: Column(
mainAxisAlignment: MainAxisAlignment.center,
children: <Widget>[
Text(
'Back',
style: Theme.of(context).textTheme.headline1,
),
Text('Click here to flip back',
style: Theme.of(context).textTheme.bodyText1),
],
),
),
));
}
@override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text('FlipCard'),
),
drawer: Drawer(
child: ListView(
padding: EdgeInsets.zero,
children: <Widget>[
DrawerHeader(
child: Text('Drawer'),
decoration: BoxDecoration(
color: Colors.blue,
),
),
futureDropdown(),
//ExpansionListTile(header: dItem.header, listOfItems: dItem.listOfItems),
],
),
),
body: Stack(
fit: StackFit.expand,
children: <Widget>[
_renderBg(),
Column(
crossAxisAlignment: CrossAxisAlignment.stretch,
children: <Widget>[
_renderAppBar(context),
Expanded(
flex: 4,
child: _renderContext(context),
),
Expanded(
flex: 1,
child: Container(),
)
],
)
],
),
);
}
}
class ExpansionListTile extends StatelessWidget {
final String header;
final List<String> listOfItems;
ExpansionListTile({this.header, this.listOfItems});
@override
Widget build(BuildContext context) {
return ExpansionTile(
title: Text(header),
children: List.generate(listOfItems.length, (index) {
return GestureDetector(
onTap: (){print('Yep i pressed shit');},
child: Text(listOfItems[index].toString()));
}));
}
}
【问题讨论】：