How to update child dropdown after parent dropdown's selection changes? - flutter

Question

So I have a column of dropdowns, each dropdown a prerequisite of the dropdown below. When Dropdown A changes its value, I'd make an API call and populate Dropdown B, Dropdown C's options are dependent on the value of B, and so on...
I accomplished this scenario fine, but the problem I'm having is when Dropdowns A to D have been selected, and I change the value of Dropdown B, Dropdowns C and D doesn't change its value.
SOS & TY

Answer 1

Refer the given example:
import 'package:flutter/material.dart';
void main() => runApp(MyApp());
/// This is the main application widget.
class MyApp extends StatelessWidget {
static const String _title = 'Flutter Code Sample';
#override
Widget build(BuildContext context) {
return MaterialApp(
title: _title,
home: Scaffold(
appBar: AppBar(title: const Text(_title)),
body: Center(
child: MyStatefulWidget(),
),
),
);
}
}
/// This is the stateful widget that the main application instantiates.
class MyStatefulWidget extends StatefulWidget {
MyStatefulWidget({Key key}) : super(key: key);
#override
_MyStatefulWidgetState createState() => _MyStatefulWidgetState();
}
/// This is the private State class that goes with MyStatefulWidget.
class _MyStatefulWidgetState extends State<MyStatefulWidget> {
String dropdownValue = 'One';
#override
Widget build(BuildContext context) {
return DropdownButton<String>(
value: dropdownValue,
icon: Icon(Icons.arrow_downward),
iconSize: 24,
elevation: 16,
style: TextStyle(color: Colors.deepPurple),
underline: Container(
height: 2,
color: Colors.deepPurpleAccent,
),
onChanged: (String newValue) {
setState(() {
dropdownValue = newValue;
});
},
items: <String>['One', 'Two', 'Free', 'Four']
.map<DropdownMenuItem<String>>((String value) {
return DropdownMenuItem<String>(
value: value,
child: Text(value),
);
}).toList(),
);
}
}