我遇到了计时问题,我从api获取数据,然后从
JSON创建一个列表.我想在结果列表视图中使用结果列表的长度作为项目计数.但是它会在itemcount上抛出null错误,然后完成处理并显示listview.我试图找到时间问题的位置以及如何处理项目和小部件,以便我可以避免错误.如果有人有任何想法我的代码存在缺陷,我的代码如下.
class Specialty extends StatefulWidget {
Specialty({Key key,this.title}) : super(key: key);
final String title;
@override
_SpecialtyState createState() => new _SpecialtyState();
}
class _SpecialtyState extends State<Specialty> {
bool _dataReceived = false;
bool _authenticated = false;
SharedPreferences prefs;
List mylist;
@override
void initState() {
super.initState();
_getPrefs();
_getSpecialty();
}
_getPrefs() async {
prefs = await SharedPreferences.getInstance();
_authenticated = prefs.getBool('authenticated');
print('AUTH2: ' + _authenticated.toString());
print('AUTHCODE2: ' + prefs.getString('authcode'));
}
_getSpecialty() async {
var _url = 'http://$baseurl:8080/support/specialty';
var http = createHttpClient();
var response = await http.get(_url);
var specialties = jsonCodec.decode(response.body);
mylist = specialties.toList();
//_dataReceived = true;
setState(() {
_dataReceived = true;
});
}
Future<Null> _onRefresh() {
Completer<Null> completer = new Completer<Null>();
Timer timer = new Timer(new Duration(seconds: 3),() {
completer.complete();
});
return completer.future;
}
@override
Widget build(BuildContext context) {
return new Scaffold(
body: new RefreshIndicator(
child: new ListView.builder(
itemBuilder: _itemBuilder,itemCount: mylist.length,),onRefresh: _onRefresh,));
}
Widget _itemBuilder(BuildContext context,int index) {
Specialties spec = getSpec(index);
return new SpecialtyWidget(spec: spec,);
}
Specialties getSpec(int index) {
return new Specialties(
mylist[index]['id'],mylist[index]['name'],mylist[index]['details'],new Photo('lib/images/' + mylist[index]['image'],mylist[index]['name']));
//return new Specialties.fromMap(mylist[index]);
}
var jsonCodec = const JsonCodec();
}
