我知道这有点混乱，并且我对flutter很陌生，我很了解状态如何在react上表现出来，但是flutter上的状态管理在数组变量上表现出不同的表现。
当我尝试使用其他方法设置状态时，它给了我不同的错误消息。我已经在这个特定的小部件上工作了一个星期，但仍然不知道我在哪里做错了。
class SurveyCard extends StatefulWidget {
final int argument;
SurveyCard({Key key, this.argument}) : super(key: key);
State<StatefulWidget> createState() {
return _Survey(argument: argument);
}
}
class _Survey extends State<SurveyCard> {
List<int> _value1=[];
int argument;
_Survey({Key key, this.argument});
int value0=0;
List<File> _file=[];
void choose(i) async {
var file;
file = await ImagePicker.pickImage(source: ImageSource.camera);
// giving me error when i take a picture.NoSuchMethodError (NoSuchMethodError: The method '[]=' was called on null. Receiver: nullTried calling: []=(0, Instance of '_File'))
setState(() => _file[i] = file);
}
//cond 1 i can't press the radio button
void _setvalue1(int value, i) {
setState(() {
_value1[i]=value;
});
}
// cond 2 doesn't work and giving me rangeerror invalid value
// _setvalue1(int value, i) {
// setState(() {
// _value1[i]=value;
// });
// }
Widget makeRadioTiles(data, index) {
List<Widget> list = new List<Widget>();
for (int i = 0; i < data.length; i++) {
int id = data[i].answerID;
list.add(new RadioListTile(
value: id,
groupValue: _value1,
// cond1
onChanged:(id) => _setvalue1(id, index),
// cond 2
// onChanged: _setvalue1(id, index),
activeColor: Colors.green,
controlAffinity: ListTileControlAffinity.trailing,
title: new Text('${data[i].answerName}'),
));
}
Column column = new Column(
children: list,
);
return column;
}
@override
Widget build(BuildContext context) {
// TODO: implement build
return BaseWidget<VesselScreenModel>(
model: VesselScreenModel(api: Provider.of(context)),
onModelReady: (model) => model.getQuestion(argument),
builder: (context, model, child) => model.busy
? Center(child: new CircularProgressIndicator())
: ListView.builder(
padding: const EdgeInsets.all(32),
scrollDirection: Axis.vertical,
shrinkWrap: true,
itemCount: model.questions.data.questions.length,
itemBuilder: (context, i) {
var dataSnapshot = model.questions;
var snapshot = dataSnapshot.data.questions[i];
return Card(
color: Colors.white,
child: Column(
children: [
Center(
child: _file == null
? Text('No image selected.')
: Image.file(_file[i]),
),
ListTile(
title: Text('${snapshot.questionName}',
style: TextStyle(
fontWeight: FontWeight.w900,
color: Colors.black))),
Column(
children: <Widget>[
makeRadioTiles(snapshot.answers, i)
],
),
Container(
padding: const EdgeInsets.only(left: 16, right: 16),
child: TextField(
decoration: InputDecoration(labelText: 'Comment'),
),
),
Align(
alignment: Alignment.centerLeft,
child: Container(
child: FlatButton(
color: Color.fromRGBO(105, 114, 100, 0),
//where i take a picture for image
onPressed: () => choose(i),
child: const Text('Upload Image',
style: TextStyle(fontSize: 15))),
),
),
],
),
);
},
));
}
}
答案 0 :(得分：0)
您正在使用固定大小的列表_value1和_file。当您知道数组索引的上限时，请考虑使用它们的大小初始化这两个列表。
为了使它正常工作，我已经对您的代码进行了一些修改。
class SurveyCard extends StatefulWidget {
final int argument;
SurveyCard({Key key, this.argument}) : super(key: key);
State<StatefulWidget> createState() {
return _Survey(argument: argument);
}
}
class _Survey extends State<SurveyCard> {
//Instead of initialzing your lists here
//initilize them inside itembuilder
List<int> _value1;
int argument;
_Survey({Key key, this.argument});
int value0=0;
List<File> _file;
void choose(i) async {
var file;
file = await ImagePicker.pickImage(source: ImageSource.camera);
// giving me error when i take a picture.NoSuchMethodError (NoSuchMethodError: The method '[]=' was called on null. Receiver: nullTried calling: []=(0, Instance of '_File'))
setState(() => _file[i] = file);
}
//cond 1 i can't press the radio button
void _setvalue1(int value, i) {
setState(() {
_value1[i]=value;
});
}
// cond 2 doesn't work and giving me rangeerror invalid value
// _setvalue1(int value, i) {
// setState(() {
// _value1[i]=value;
// });
// }
Widget makeRadioTiles(data, index) {
List<Widget> list = new List<Widget>();
for (int i = 0; i < data.length; i++) {
int id = data[i].answerID;
list.add(new RadioListTile(
value: id,
groupValue: _value1,
// cond1
onChanged:(id) => _setvalue1(id, index),
// cond 2
// onChanged: _setvalue1(id, index),
activeColor: Colors.green,
controlAffinity: ListTileControlAffinity.trailing,
title: new Text('${data[i].answerName}'),
));
}
Column column = new Column(
children: list,
);
return column;
}
@override
Widget build(BuildContext context) {
// TODO: implement build
return BaseWidget<VesselScreenModel>(
model: VesselScreenModel(api: Provider.of(context)),
onModelReady: (model) => model.getQuestion(argument),
builder: (context, model, child) => model.busy
? Center(child: new CircularProgressIndicator())
: ListView.builder(
padding: const EdgeInsets.all(32),
scrollDirection: Axis.vertical,
shrinkWrap: true,
itemCount: model.questions.data.questions.length,
itemBuilder: (context, i) {
//initialize your lists here
_value1 = List<int>(i);
_file = List<File>(i);
var dataSnapshot = model.questions;
var snapshot = dataSnapshot.data.questions[i];
return Card(
color: Colors.white,
child: Column(
children: [
Center(
child: _file == null
? Text('No image selected.')
: Image.file(_file[i]),
),
ListTile(
title: Text('${snapshot.questionName}',
style: TextStyle(
fontWeight: FontWeight.w900,
color: Colors.black))),
Column(
children: <Widget>[
makeRadioTiles(snapshot.answers, i)
],
),
Container(
padding: const EdgeInsets.only(left: 16, right: 16),
child: TextField(
decoration: InputDecoration(labelText: 'Comment'),
),
),
Align(
alignment: Alignment.centerLeft,
child: Container(
child: FlatButton(
color: Color.fromRGBO(105, 114, 100, 0),
//where i take a picture for image
onPressed: () => choose(i),
child: const Text('Upload Image',
style: TextStyle(fontSize: 15))),
),
),
],
),
);
},
),
);
}
}