Flutter | Pass value from child to parent - flutter

Question

I need a DropdownButton with items depending on another DropdownButton. Sounds a bit confusing but it isnt. Here is my code with comments at the important parts in order to understand my intention.
Parent
class Parent extends StatefulWidget {
const Parent({ Key? key }) : super(key: key);
#override
State<Parent> createState() => _ParentState();
}
class _ParentState extends State<Parent> {
#override
Widget build(BuildContext context) {
return SafeArea(
child: SizedBox(
width: 500,
height: 500,
child: Column(
children: const [
// Main
DropDownWidget(collection: "MainCollection",),
// Depending
DropDownWidget(collection: ""), // Collection should equals value from Main DropDownWidget
],
),
),
);
}
}
Child
class DropDownWidget extends StatefulWidget {
final String collection;
const DropDownWidget({Key? key, required this.collection}) : super(key: key);
#override
State<DropDownWidget> createState() => _DropDownWidgetState();
}
class _DropDownWidgetState extends State<DropDownWidget> {
var selectedItem;
#override
Widget build(BuildContext context) {
return StreamBuilder<QuerySnapshot>(
stream: FirebaseFirestore.instance
.collection(widget.collection)
.snapshots(),
builder: (context, snapshot) {
if (!snapshot.hasData || snapshot.hasError) {
return const CircularProgressIndicator();
} else {
var length = snapshot.data?.docs.length;
List<DropdownMenuItem<String>> items = [];
for (int i = 0; i < length!; i++) {
DocumentSnapshot snap = snapshot.data!.docs[i];
items.add(DropdownMenuItem(
child: Text(snap.id),
value: snap.id,
));
}
return DropdownButtonFormField<String>(
onChanged: (value) {
setState(() {
selectedItem = value;
// ********************
// PASS value TO PARENT
// ********************
});
},
value: selectedItem,
items: items);
}
});
}
}
When the Main DropdownButton changes its value, it should pass that to my parent in order to change the focused collection of my depending DropdownButton. I already solved that problem by throwing all the code in one class buts that not the way I want to go.
So maybe you can help me out :)
Thanks

Answer 1

Create an argument ValueChanged<String> onSelectItem in your child. Call the method when the value changes.
Then in your parent, you provide a function that needs to be called when the value changes in your child.