flutter - 在“无数据”小部件的情况下拉动以刷新

问题描述

我需要帮助，请我有一个 RefreshIndicator，当数据库中有数据时加载 ListView 但是如果表为空而不是 ListView，我想让小部件返回文本小部件“无数据”。但是当表为空时出现错误
_TypeError（类型'String'不是'Iterable'类型的子类型）
并且会出现在刷新方法中我不知道我应该做什么我感谢任何帮助提前谢谢. 这是页面的 UI

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),
                                 ),
                               ),
                             ),
                           ),
                         ],
                       ))),
                    );
               },
          );
 }

刷新方法

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 "";
  }

标签： flutterdartpull-to-refreshflutter-widgetflutter-futurebuilder

flutter - 在“无数据”小部件的情况下拉动以刷新

问题描述

解决方案

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