FLutter：迭代列表时在 null 上调用了方法“[]”

Question

这是我到现在为止的源代码。您能告诉我哪里出了问题以及为什么会出现此错误吗？

任何帮助将不胜感激。谢谢！

错误是：

Data[0] 出现错误，它显示 Flutter：迭代列表导入 'package:flutter/material.dart' 时，方法 '[]' 在 null 上被调用；

class MyGetHttpDataState extends State<MyGetHttpData> { 

    final String url = "*******";
    List data, a; int index; // Function to get the JSON data 

    Future<String> getJSONData() async {
        var response = await http.get(url);
        print(response.body);
        setState(() {
           json.decode(response.body);
           data = dataConvertedToJSON['data']; index = 0;
        });
        return "Successfull";
    }

    @override
    Widget build(BuildContext context) {
        return new MaterialApp( 
          home: new Scaffold( 
            appBar: new AppBar( title: new Text('List Test'), ), 
            body: new Center( 
              child: Column( 
                mainAxisAlignment: MainAxisAlignment.center, 
                children: <Widget>[
                  for (var name in data[0]['INCI']) Text(name)
                ], ), ), )); 
    } 

    @override
    void initState() {
      super.initState();
      this.getJSONData(); 
    }
}

Answer 1

只需将您的代码更改为这个！

Future<String> getJSONData() async {
    var response = await http.get(url);
    setState(() {
       var dataConvertedToJSON = json.decode(response.body);
       data = dataConvertedToJSON['data'];
       data = data[0]['INCI'];
    });
    return "Successfull";
}

@override
Widget build(BuildContext context) {
    return new MaterialApp( 
      home: new Scaffold( 
        appBar: new AppBar( title: new Text('List Test'), ), 
        body: new Center( 
          child: data != null ? Column(
            mainAxisAlignment: MainAxisAlignment.center, 
            children: <Widget>[
              for (var name in data) Text(name)
            ], 
          ) : new CircularProgressIndicator(), 
        ), 
      )
    ); 
}