颤振 - 尝试解析本地 json 数据时"Range error (length)"

Question

我有一个包含文本的 JSON 文件，每个句子都在一个单独的 JSON 对象中，用户应该能够在带有next()和previous()的 sentenes 之间导航，但是当应用程序加载时，我收到此错误：

范围

错误(索引(：无效值：有效值范围为空：0

直到我按下屏幕上的任何其他按钮，此时文本加载并显示。

卡片本身是一个有状态的小部件，这是我的代码：

class _BottomCardsState extends State<BottomCards>{
bool isLoadingEnded = false;
Future<Null> getAllData() async{
await DefaultAssetBundle.of(context).loadString('assets/json/data.json').then((response){
isLoadingEnded = true;
var decodedData = json.decode(response);
for(Map d in decodedData){
dataList.add(Data.fromJson(d));
}      
});
}
@override
void initState() {
super.initState();
getAllData();
}
int dataIndex = 0;
@override
Widget build(BuildContext context) {
int myNbr = dataList[dataIndex].id;
return Container(
child: Material(
color: Colors.transparent,
child: Card(
margin: EdgeInsets.symmetric(horizontal: 10.0),
elevation: 6.0,
child: Container(
alignment: Alignment.topCenter,
padding: EdgeInsets.symmetric(horizontal: 12.0,),
child: Column(
children: <Widget>[
Row(
children: <Widget>[
IconButton(                  
splashColor: gradientStart,
icon: Icon(Icons.keyboard_arrow_left,),
onPressed: () {_previous();},
),
IconButton(
splashColor: gradientStart,
icon: Icon(Icons.keyboard_arrow_right,),
onPressed: () {_next();},
),
],
),
SizedBox(height: 4.0,),
isLoadingEnded == true ? Container(
child: Column(
children: <Widget>[
Row(
mainAxisAlignment: MainAxisAlignment.start,
mainAxisSize: MainAxisSize.max,
children: <Widget>[
Expanded(                  
child: InkWell(
splashColor: Colors.lightBlue[100],
onTap: (){},
//the paragraph gets displayed here
child: Text(dataList[dataIndex].paragraph,
),
),
],
),
SizedBox(height: 8.0,),
Row(
mainAxisAlignment: MainAxisAlignment.end,
mainAxisSize: MainAxisSize.max,
children: <Widget>[
Chip(
backgroundColor: secondaryDark,
label: Text('Number: $myNbr',
style: TextStyle(color: Colors.white, fontSize: 10.0, fontWeight: FontWeight.w500),),
),
],
),
],
),
): Center(child: loadingIndicator(),),
SizedBox(height: 6.0),
],
),
),
),
),
);
}
}

' 我的 JSON 格式：

{
"id": 1,
"paragraph": "lorem ipsum"
},
...

Answer 1

您需要等到数据填满。

更改 getAllData 方法。喜欢

Future<List<Data>> getAllData() async{
var response = await DefaultAssetBundle.of(context).loadString('assets/json/data.json')
var decodedData = json.decode(response);
for(Map d in decodedData){
dataList.add(Data.fromJson(d));
}  
return dataList;
}

现在等待构建方法。喜欢

@override
Widget build(BuildContext context) {
return FutureBuilder<List<Data>>(
future: getAllData(),
builder: (context, snapshot) {
if (snapshot.hasData) {
print("Here you can get data "+snapshot.data.toString());
//you can put your ui here
} else {
print("Waiting mode");
return Container(
color: Colors.blue,
);
}
},
)
}

Answer 2

import 'package：flutter/services.dart' show rootBundle;

秋天的第一天，您的数据就像一张地图，您正在尝试存储在列表中。 正如我所看到的，您的数据是地图的类型。

{
"id": 1,
"paragraph": "lorem ipsum"
}
Future<void> getAllData() async {
final res= await rootBundle.loadString('assets/config.json');
final json = jsonDecode(res.body);
var parse = json as Map; 
Data data=Data.fromJson(parse);
}

如果包含 JSON 列表数据，则

[
{
"id": 1,
"paragraph": "lorem ipsum"
},
{
"id": 1,
"paragraph": "lorem ipsum"
}
]

然后

Future<void> getAllData() async {
final res= await rootBundle.loadString('assets/config.json');
final json = jsonDecode(res.body);
var parse = json as List;
parse.forEach((d){ 
dataList.add(Data.fromJson(d));
});
}