颤动下拉按钮

Question

I try to display categories data in dropdownbutton , when I choose category I get this error,

items == null || items.isEmpty || value == null ||

code DropDownButton :

    class _DropDownButtonState extends State<DropDownButton> {
  final CollectionReference categoryData = Firestore.instance
      .collection('category')
      .document('house')
      .collection('subCategory');
  Stream<List<Categories>> categories;
  Categories _currentCategory;
  @override
  void initState() {
    categories = categoriesData;
    super.initState();
  }

  @override
  Widget build(BuildContext context) {
    return StreamBuilder<List<Categories>>(
        stream: categories,
        builder: ((context, snapshot) {
          if (!snapshot.hasData) return CircularProgressIndicator();
          return DropdownButton(
            hint: Text('choose category'),
            value: _currentCategory,
            items: snapshot.data
                .map((doc) => DropdownMenuItem(
                      child: Text(doc.categoryname),
                      value: doc,
                    ))
                .toList(),
            onChanged: (doc) => setState(() {
              _currentCategory = doc;
              print(_currentCategory.categoryname);
            }),
          );
        }));
  }

  Future createHouseCategory(_categorynameController) async {
    var id = Uuid();
    String categoryId = id.v1();
    await categoryData
        .document(categoryId)
        .setData({'categoryname': _categorynameController});
  }

  List<Categories> _categoriesDataFromSnapshot(QuerySnapshot snapshot) {
    return snapshot.documents.map((doc) {
      return Categories(
        categoryname: doc.data['categoryname'],
      );
    }).toList();
  }

  Stream<List<Categories>> get categoriesData {
    return categoryData.snapshots().map(_categoriesDataFromSnapshot);
  }


}

Answer 1

Just check out this link where I have solved the question for the dropdown :

Dropdown Button wont change

maybe you are not giving the desired parameters to the value Field, that's why it is not getting the index to show in the dropdown button. let me know if it works.

If you have any issue just give me the JSON sample, maybe we can work on it