Flutter/Dart: Handling Dropdown changes within a ListView.builder, Dropdown button not updating,

I ended up wrapping each dropdown widget (in List<Widget>) with a statefulbuilder so when setstate is called from each widget only that widget is updated but one can still udate the entire tree if needed. In this way setState is called from within a build as per anmol.majhail comments.

import 'package:flutter/material.dart';class FormEG extends StatefulWidget {  @override  _FormEGState createState() => new _FormEGState();}class _FormEGState extends State<FormEG> {  List<String> _listValues;  List<DropdownMenuItem<String>> _items;  List<Widget> _widgets;  @override  void initState() {    _listValues = new List<String>();    setDefaults();    setWidgets();    super.initState();  }  @override  Widget build(BuildContext context) {    print("built");    return new Scaffold(        body: new ListView.builder(          itemCount: _widgets.length,          itemBuilder: (context, index) {        return _widgets[index];      },    ));  }  void setDefaults() {    _listValues.add("b");  }  void setWidgets() {    setMenuItems();    _widgets = new List<Widget>();    _widgets.add(      new StatefulBuilder(        builder: (BuildContext context, StateSetter setState) {          return new DropdownButton<String>(            value: _listValues[0],            items: _items,            onChanged: (String newValue) {              setState(() {                _listValues[0] = newValue;              });            },          );        },      ),    );  }  void setMenuItems() {    _items = new List<DropdownMenuItem<String>>();    _items.add(new DropdownMenuItem(child: Text("a"), value: "a"));    _items.add(new DropdownMenuItem(child: Text("b"), value: "b"));    _items.add(new DropdownMenuItem(child: Text("c"), value: "c"));    _items.add(new DropdownMenuItem(child: Text("d"), value: "d"));  }}

Following Code Works Well. Because SetSate Calls the Build method Again & DropdownButton is Drawn again. In your Code DropdownButton is placed at _widgets[0] value & this Value Stays Static through the code cycle. Even after Calling SetState it will remain same - because SetState wont update _widgets[0] value - it will only call Build Method Again.

@override  Widget build(BuildContext context) {    return new Scaffold(        body: new ListView.builder(      itemCount: _widgets.length,      itemBuilder: (context, index) {        return DropdownButton<String>(          value: _listValues[0],          items: _items,          onChanged: (newValue) {            setState(() {              _listValues[0] = newValue;            });          },        );      },    ));  }

You could try just using a List and update the List dynamically and then setState.

ListView(                  shrinkWrap: true,                  scrollDirection: Axis.vertical,                  children: dropDownList),            ),

Then update it based on a trigger/event.

 _buildDropDownList() {     if (dropDownEnabled) {       setState (() {         dropDownList.addAll([1,2,,4,5])       });       } else {        setState (() {         dropDownList = [];      });       }