flutter dropdownbutton won't keep answer after scrolling

Question

i'm crating an app where the user can make different choices from a list of questions , just the dropdownbutton won't keep the chosen answers after the user scrolls down to the other questions check the GIF

i' working with the Provider state management system , here is the code :

import 'package:flutter/material.dart';

class ChoiceHandler extends ChangeNotifier {
  final List<String> _dropdownElements = ['Not Done', 'Partially Done', 'Done'];
  List<String> get dropdownElement => _dropdownElements;
  late String _selectedItemValue;
  String get selected => _selectedItemValue;

  selectedValues(String s) {
    _selectedItemValue = s;
    notifyListeners();
  }
}

and here is the dropdownbutton widget code :

Expanded(
            child: ListView.builder(
              itemCount: propositions.length,
              itemExtent: 50.0,
              itemBuilder: (BuildContext context, index) {
                String dropdownValue = "Not Done";

                return ListTile(
                    title: Text(propositions[index]),
                    trailing: Consumer<ChoiceHandler>(
                      builder: (_, provider, __) {
                        return DropdownButton<String>(
                          value: dropdownValue,
                          onChanged: (newValue) {
                            dropdownValue = newValue as String;
                            Provider.of<ChoiceHandler>(context, listen: false)
                                .selectedValues(dropdownValue);

                            print((propositions[index]) + "  " + newValue);
                            dropdown_answer.add(dropdownValue);
                          },
                          items: provider.dropdownElement
                              .map<DropdownMenuItem<String>>((String value) {
                            return DropdownMenuItem<String>(
                              value: value,
                              child: Text(value),
                            );
                          }).toList(),
                        );
                      },
                    ) //_dropdown(index),

                    );
              },
            ),

for the dropdown_answer, it's a variable where storing values to export them to an excel file — Benderradji Khireddine, Jun 01 '22 at 08:44
i've done everthing that avoid rebuilding but it still rebuild it ,even with "Provider.of(context, listen: false) .selectedValues(dropdownValue);" it still rebuilds the button — Benderradji Khireddine, Jun 06 '22 at 15:44
@BenderradjiKhireddine Did you find any solution for this?? Me also having same kind of problem here https://stackoverflow.com/questions/75396994/flutter-dropdownbuttonformfield2-selected-item-changes-to-initial-value-on-scr?noredirect=1#comment133037622_75396994 — KJEjava48, Feb 10 '23 at 10:04
@YeasinSheikh how & where should I use AutomaticKeepAliveClientMixin?? — KJEjava48, Feb 10 '23 at 10:39
@KJEjava48 hello , nope i didn't find a fix for that dude (i gave gave the project as it is, the client accept it ) , but i think the problem is in the rebuilding of the widgets — Benderradji Khireddine, Feb 10 '23 at 17:15

score 2 · Answer 1 · answered Feb 13 '23 at 16:19

don't intialize a variable like this String dropdownValue = "Not Done"; in listview builder. just add your status variable in your listing object

class Document {
 String title;
 String data;
 String status;
  Document({
    required this.title,
    required this.data,
    this.status="Not Done",
  });
}

then use

 List<Document> propositions=[];

with

Expanded(
            child: ListView.builder(
              itemCount: propositions.length,
              itemExtent: 50.0,
              itemBuilder: (BuildContext context, index) {

               // now don't need to user this variable
               // String dropdownValue = "Not Done";

                return ListTile(
                    title: Text(propositions[index]),
                    trailing: Consumer<ChoiceHandler>(
                      builder: (_, provider, __) {
                        return DropdownButton<String>(
                          // instead use status property from propositions[index] object
                          value: propositions[index].status,
                          onChanged: (newValue) {
                            propositions[index].status = newValue as String;
                            Provider.of<ChoiceHandler>(context, listen: false)
                                .selectedValues(propositions[index].status);

                            print((propositions[index]) + "  " + newValue);
                            dropdown_answer.add(propositions[index].status);
                          },
                          items: provider.dropdownElement
                              .map<DropdownMenuItem<String>>((String value) {
                            return DropdownMenuItem<String>(
                              value: value,
                              child: Text(value),
                            );
                          }).toList(),
                        );
                      },
                    ) //_dropdown(index),

                    );
              },
            ),

and status value will be stored and maintain status even when widget re-builds.

flutter dropdownbutton won't keep answer after scrolling

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