So I have managed to fetch the names of the folder and store them in a list. But the problem I am facing is is the list gets called twice so I tend to have duplicate items in my list view. I've asked similar questions about this but the solutions given don't work on my side. I know the problem is me calling the getFolders() in the future(which is a bad practice) but that is the only way my code actually work. When I change my list to a type Future I can't use the .add() functionality. Below is my code:

Here is where I have declared my list:

class Semester extends StatefulWidget {
  final String value;
  const Semester({Key? key, required this.value}) : super(key: key);
  @override
  State<Semester> createState() => _SemesterState();
}

class _SemesterState extends State<Semester> {

  late List<String> courses = []; // possible culprit
  Future<List<FirebaseFolder>>? listResult;
  Future<List<String>> getFolders() async {
    final storageRef = FirebaseStorage.instance.ref().child(widget.value);
    final listResult = await storageRef.listAll();
    for (var prefix in listResult.prefixes) {
      courses.add(prefix.name);
    }
    return courses;
  }

  @override
  void initState() {
    // TODO: implement initState
    super.initState();
    getFolders();
  }

So when I change the courses to Future<List> I can't use the courses.add(prefix.name) since it says it is not of type future: And as you can see below I had to use the getFolder() function on my future for it to display contents on my listview, (NOTE: even if I use it on instantiating the result is still same:)

 @override
  Widget build(BuildContext context) {
    return Scaffold(
      backgroundColor: Colors.white,
      appBar: AppBar(
        leading: kIconButton(),
        elevation: 0,
        centerTitle: true,
        title: const Text("Semester", style: kTitleStyle),
        backgroundColor: Colors.white,
      ),
      body: FutureBuilder(
        future: getFolders(), // possible culprit
        builder: (context, snapshot) {
          switch (snapshot.connectionState) {
            case ConnectionState.waiting:
              return const Center(
                child: spinkitLines,
              );
            default:
              return Column(
                children: [
                  const SizedBox(
                    height: 20.0,
                  ),
                  const Center(
                    child: Text(
                      'Tap to choose course',
                      style: kPlaceholderStyle,
                    ),
                  ),
                  const SizedBox(
                    height: 30.0,
                  ),
                  Expanded(
                    child: ListView.builder(
                        itemCount: courses.length,
                        itemBuilder: (context, index) {
                          return Padding(
                            padding: const EdgeInsets.all(8.0),
                            child: GestureDetector(
                              onTap: () {
                                String passedValue = widget.value;
                                String course = courses[index];
                                String value = "$passedValue""/""$course";
                                Get.to(() => CourseContent(value: value, courseChosen: course,));
                              },
                              child: Container(
                                height: 80,
                                decoration: const BoxDecoration(
                                  color: Colors.black,
                                  borderRadius:
                                      BorderRadius.all(Radius.circular(20)),
                                  boxShadow: [
                                    BoxShadow(
                                        color: Color.fromARGB(75, 0, 0, 0),
                                        blurRadius: 4,
                                        spreadRadius: 0,
                                        offset: Offset(0, 4))
                                  ],
                                ),
                                child: Center(
                                  child: Padding(
                                    padding: const EdgeInsets.all(5.0),
                                    child: Text(
                                      courses[index],
                                      style: kCardTitleStyle,
                                    ),
                                  ),
                                ),
                              ),
                            ),
                          );
                        }),
                  ),
                ],
              );
          }
        },
      ),
    );
  }
}

So I am looking for a way to fetch the list(folders prefixes) and display them in a list view. What I have tried above works but sometimes it displays duplicates which I can tell the getfolder() is being called multiple times.. Help me solve this.

CodePudding user response：

So I came up with a clever and simple solution. I wrapped my for loop with if to check if the array is empty. if not it won't run that code!

  late List<String> courses = [];
  Future<List<FirebaseFolder>>? listResult;
  Future<List<String>> getFolders() async {
    final storageRef = FirebaseStorage.instance.ref().child(widget.value);
    final listResult = await storageRef.listAll();
    if(courses.isEmpty){
    for (var prefix in listResult.prefixes) {
      courses.add(prefix.name);
    }
    }
    return courses;
  }

CodePudding user response：

It is possible to make sure you get the data from snapshot like this way as shown on blow. Note: elements in that child is an example.

        if(!snapshot.hasData) {
          return Center(
            child: const CircularProgressIndicator(
              backgroundColor: Colors.lightBlue,
            ),
          );
        }