DropdownButton is not changing the value on onChanged - dart

Question

The DropdownButton is not changing the value of dropdown after another selection is made from the dropdown. Below is my code.
Flexible(
child: Padding(
padding: EdgeInsets.fromLTRB(0.0, 0.0, 10.0, 0.0),
child: DropdownButton(
hint: Text('Select'),
items: list_dropdown,
onChanged: (val) {
setState(() {
wd = val;
});
},
value: wd,
)),
)
In the initState I'm setting the value variable
#override
void initState() {
// TODO: implement initState
super.initState();
wd = 0;
}
while I create the variale in the global scope
int wd;
Where am I going wrong?

Answer 1

Why did you create a variable in the global scope? If you want to mutate your variable called wd with setState(), you have to put it in your state class.
class App extends StatefulWidget {
#override
_AppState createState() => _AppState();
}
class _AppState extends State<App> {
// Here wd in my state class
int wd = 0;
#override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text("Cat Attack"),
),
body: Center(
child: DropdownButton(
value: wd,
onChanged: (val) {
setState(() {
wd = val;
});
},
items: [
DropdownMenuItem(
child: Text('1'),
value: 1,
),
DropdownMenuItem(
child: Text('2'),
value: 2,
),
],
),
));
}
}
You can override the value of wd in initState(), once you've defined in state.
class _AppState extends State<App> {
int wd;
#override
void initState() {
super.initState();
wd = 2;
}
Keep in mind that, your "value" for DropdownButton should be set to 'null' or be one from the values list. So if you set it to 5, rather then 1, 2 or null, which are the values in my DropdownMenuItem's, you will get this error:
I/flutter (15227): ══╡ EXCEPTION CAUGHT BY WIDGETS LIBRARY ╞═══════════════════════════════════════════════════════════
I/flutter (15227): The following assertion was thrown building App(dirty, state: _AppState#30354):
I/flutter (15227): 'package:flutter/src/material/dropdown.dart': Failed assertion: line 560 pos 15: 'items == null ||
I/flutter (15227): items.isEmpty || value == null || items.where((DropdownMenuItem item) => item.value ==
I/flutter (15227): value).length == 1': is not true.