I made a class that receives the IDs of data in firebase firestore and shows the contents using Listview.builder. I confirmed that the class correctly gets data from previous class and I cannot see any error message, but the result shows nothing.

class list_topic extends StatefulWidget{
  const list_topic({Key? key, required this.topic_send}) : super(key: key);
  final List<dynamic> topic_send ;
  @override
  _list_topicState createState() => _list_topicState();
}

class _list_topicState extends State<list_topic> {
  void initState() {
    super.initState();
    getData();
  }
  List<dynamic> topicAll = [];
  List<String> topicTitle = [];
  List<String> topicId = [];
  List<String> topicAbstract = [];
  List<String> topicWriter = [];
  List<int> topicVoteLeft = [];
  List<int> topicVoteRight = [];

  Future<void> getData() async {
    List<dynamic> topicReceived = widget.topic_send;
    for (int i = 0; i < topicReceived.length; i  ) {
      FirebaseFirestore.instance
          .collection('topic')
          .doc(topicReceived[i].toString())
          .get()
          .then((DocumentSnapshot doc) {
        final data_ = doc.data() as Map<String, dynamic>;
       // Future.delayed(Duration(milliseconds : 0),(){
          String abs = data_['abstract'];
          String title = data_['title'];
          String writer = data_['writer'];
          int vl = data_['vote_left'];
          int vr = data_['vote_right'];
          topicId.add(topicReceived[i]);
          topicTitle.add(title);
          topicAbstract.add(abs);
          topicWriter.add(writer);
          topicVoteLeft.add(vl);
          topicVoteRight.add(vr);
          topicAll.add(topicTitle);
          topicAll.add(topicAbstract);
          topicAll.add(topicWriter);
          topicAll.add(topicVoteLeft);
          topicAll.add(topicVoteRight);
          print('313131313131');
          print(topicId.length);
          print(topicTitle.length);
          print(topicAbstract.length);
          print('24242424242424');

      //  });
      });
    }
    //return topicAll;
  }
  @override
  Widget build(BuildContext context) {
   // getData();

    return Scaffold(
      appBar: AppBar(
        backgroundColor: Colors.white,
        toolbarHeight: 1.0,
      ),

      body:
      Column(
        mainAxisAlignment: MainAxisAlignment.center,
        crossAxisAlignment: CrossAxisAlignment.center,
        children: [
          Align(
            alignment: Alignment.topLeft,
            child:SizedBox(
              height:30,
              width:20,
              child:
              TextButton(onPressed: (){

                Navigator.of(context).pop();

              },
                  style: TextButton.styleFrom( primary: Colors.brown,),
                  child: Icon(Icons.arrow_back)
              ),
            ),
          ),
          Padding(padding: EdgeInsets.symmetric(vertical: 10)),

          TextField(
            //focusNode: _focus,
            keyboardType: TextInputType.text,
            onChanged: (text){
              //  _streamSearch.add(text);
            },
            decoration: InputDecoration(
              //hintText: lang(0),
                border: InputBorder.none,
                icon: Padding(
                    padding: EdgeInsets.only(left: 13),
                    child: Icon(Icons.search))),
          ),

          SizedBox(
            height:MediaQuery.of(context).size.height*0.77,
            width:MediaQuery.of(context).size.width*0.8,

            child: ListView.builder(
              shrinkWrap: true,
              physics: BouncingScrollPhysics(),
              scrollDirection: Axis.vertical,
              itemCount: topicTitle.length,
              itemBuilder: (context,index){
                return GestureDetector(
                    onTap: (){
                      navi_to_debates(context,topicId[index]);
                      },
                    child:customCardCategory_topic(context, topicTitle[index], topicAbstract[index], Icons.topic_outlined, '22.PNG',topicVoteLeft[index],topicVoteRight[index])
                )
                ;
              },
            ),
          )
        ],
      ),
    );



  }
}

The result screen is shown in below :

However, If I click the Textfield for searching, the Listview suddenly works.

Since Im very new to flutter I cannot even understand why this happens and why no error message appears. Can anybody tell my what I did wrong ?

CodePudding user response：

You need to call setState to update the UI. You can do

  @override
  void initState() {
    super.initState();
    getData().then((value) => setState((){}));
  }

Or

  Future<void> getData() async {
    ....
    setState(() {});
  }

And use

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      resizeToAvoidBottomInset: true,
      appBar: AppBar(
        backgroundColor: Colors.white,
        toolbarHeight: 1.0,
      ),
      body: SingleChildScrollView(
        child: Column(