pull to refresh in case 'No data' widget - flutter

Question

I need help in this please i have a RefreshIndicator that loads a ListView when there is data in the database however I want to make the widget return Text widget 'no data' if the table empty instead of the ListView.
but the when the table is empty it error appear
_TypeError (type 'String' is not a subtype of type 'Iterable')
and that will appear in the refresh method i don't know what should i do i appreciate any help thanks in advance.
this the UI for the page
class _onlineResultTab extends State<onlineResultTab> {
List<ResultsModelClass> resultslist = new List();
List<CoursesModelClass> coursesist = new List();
ResultsModelClass resultsModelClass;
CoursesModelClass courseModelClass;
final GlobalKey<RefreshIndicatorState> refreshKey = GlobalKey<RefreshIndicatorState>();
DataApiProvider dataApiProvider = new DataApiProvider();
Widget build(BuildContext context) {
return Scaffold(
body: RefreshIndicator(
key: refreshKey,
onRefresh: refreshList,
child: _resultwidget(context),
),
);
}
fetchResultDetails() async {
final allRows = await DbHelper.mydb.getOnlineResultList();
allRows.forEach((row) => {
resultsModelClass = ResultsModelClass(
"",
row["Res_Stud_Index"],
row["Res_Stud_Name"],
row["Res_Sem"].toString(),
"",
"",
row["Res_Batch"],
row["Res_Courses"],
row["Res_Grade"],
row["Res_GPA"].toString(),
row["Res_CGPA"],
row["Res_Status"],
row["faculty_desc_e"],
row["major_desc_e"]),
resultslist.add(resultsModelClass)
});
if (this.mounted) {
setState(() {});
}
}
fetchCourse() async {
final allRows = await DbHelper.mydb.getResultcoursesList();
allRows.forEach((row) => {
courseModelClass = CoursesModelClass(
row["Res_Courses"],
row["Res_Grade"],
),
coursesist.add(courseModelClass)
});
if (this.mounted) {
setState(() {});
}
}
List<String> listHeader = ['Student Results Details'];
Widget _resultwidget(context) {
final _size = MediaQuery.of(context).size;
return resultslist.length == 0
? ListView.builder(
controller: ScrollController(),
itemCount: 1,
itemBuilder: (context, index) {
return Center(
child: Padding(
padding: EdgeInsets.only(top: _size.height * 0.4),
child: Text(
"No Result Details !",
style: TextStyle(fontSize: 20),
),
));
},
physics: AlwaysScrollableScrollPhysics(),
)
: new ListView.builder(
itemCount: listHeader.length,
itemBuilder: (context, index) {
//var _size = MediaQuery.of(context).size;
return SingleChildScrollView(
child: Center(
child: Padding(
padding: EdgeInsets.only(bottom: _size.height * 0.02),
child: Column(
children: [
Card(
elevation: 20,
margin: EdgeInsets.symmetric(
horizontal: _size.width * 0.005,
),
child: Container(
height: 50.0,
decoration: BoxDecoration(
color: Theme.of(context).backgroundColor),
child: Center(
child: Text(
'Semester ' +
resultslist[0].Res_Sem +
' Result ',
style: TextStyle(
color: Colors.white,
fontSize: 17,
fontWeight: FontWeight.bold),
),
),
),
),
],
))),
);
},
);
}
the refresh method
Future<String> refreshList() async {
refreshKey.currentState?.show(atTop: false);
//await Future.delayed(Duration(seconds: 10));
var studentIndex;
final allRows = await DbHelper.mydb.MainInfoCehck();
allRows.forEach((row) => {
row["Stud_Index"],
studentIndex = row["Stud_Index"].toString()
//print( row["Stud_Index"].toString())
});
print(studentIndex);
//void refreshResult(String studentIndex)async{
await dataApiProvider.refresh_result(studentIndex);
// }
if (this.mounted) {
setState(() {
coursesist.clear();
resultslist.clear();
fetchResultDetails();
fetchCourse();
});
}
return null;
}
Future<String> refresh_result(String studentIndex) async {
var url = main_urll + "?studentIndex=" + studentIndex.trim();
final response = await http.get(url);
List<ResultDetailsModel> ResulttDetailsListModel = [];
final resultInfo = jsonDecode(response.body)['result_info'];
DbHelper.mydb.deleteTableData("Result");
print('Result informations : ' + resultInfo.toString());
for (Map i in resultInfo) {
ResulttDetailsListModel.add(ResultDetailsModel.fromJson(i));
DbHelper.mydb.saveResultDetails(ResultDetailsModel.fromJson(i));
}
return "";
}

Answer 1

Please check if
resultslist == null or resultslist.isNotEmpty()
for Handling empty list