应用异步取得Future<T>
在flutter我的项目中应用async await异步获取数据时，会返回一个Future<T>类型的数据，然而将其应用在widget中，会有一个问题：在statefulWidget中应用变量接管值，会呈现无奈赋值的状况
///index.dart class Index extends StatefulWidget { Index({Key key}) : super(key: key); @override _IndexState createState() => _IndexState();} class _IndexState extends State<Index> { List<Widget> _temps; String _studentId = "abcd"; String _token = "lkjncasfmalknfadwSadwawf1dawd"; @override void initState() { super.initState(); _temps = _getClassItems(getOneDaylessons(_dates, _studentId, _token)); } var _dates = initDate(); void _getDates(value) { _dates = DateFormat('EEE', "en_US").format(value).toString(); setState(() { _temps = _getClassItems(getOneDaylessons(_dates, _studentId, _token)); }); } List<Widget> _getClassItems(List<Widget> classItems) { if (classItems.isEmpty) { return [ Container( height: 60, child: Center( child: Text("今日暂无课程"), ), ) ]; } else { return classItems; } } @override Widget build(BuildContext context) { return Scaffold( body: Container( child: Column( children: _temps,//报错处 ), ) ) } ///getOneDaylessons.dart List<Widget> getOneDaylessons(String date, String studentId, String token) { ClassResponseData _data; getTimeTableFromStudentID(studentId, token) .then((v) => {_data=v}); List<ClassItemViewModel> datas = getADayClasses(data); List temp = datas .map((e) { if (e.date == date) { return ClassItem(data: e); } }) .toList() .where((element) => element != null) .toList(); return temp;}//运行我的项目报错_temps是null解决方案
将getOneDaylessons同样应用async包装，返回Future<T>到index.dart.在index.dart中，应用FutureBuilder，取值
///getOneDaylessons.dartFuture<List<Widget>> getOneDaylessons( String date, String studentId, String token) async { ClassResponseData response = await getTimeTableFromStudentID(studentId, token); List<ClassItemViewModel> datas = getADayClasses(response); List temp = datas .map((e) { if (e.date == date) { return ClassItem(data: e); } }) .toList() .where((element) => element != null) .toList(); return temp;}///index.dart..._temps = _getClassItems();...Future<List<Widget>> _getClassItems() async { List<Widget> classItems = await getOneDaylessons(this._dates, this._studentId, this._token); if (classItems.isEmpty) { return [ Container( height: 60, child: Center( child: Text("今日暂无课程"), ), ) ]; } else { return classItems; } } @override Widget build(BuildContext context) { return Scaffold( body: Container( child: Container( child: FutureBuilder( future: _temps, builder: // ignore: missing_return (BuildContext context, AsyncSnapshot snapshot) { if (snapshot.connectionState == ConnectionState.done) { if (snapshot.hasError) { return Text(snapshot.error.toString()); } return Column(children: snapshot.data); } return CircularProgressIndicator(); }), ), ) }