How to detect focus in children from a parent widget - flutter

Question

In flutter,
How can a parent widget know if a child among many children widgets has received focus? For example, Can we know if a child in a Row widget's children has received focus?
Can I detect this focus before the child widget receives it?

Answer 1

It actually depends on your take and which architecture you wanna follow.
This snippet that I'm posting uses NotificationListener, a custom notification and a custom child widget. This might work for an application like a print or a callback, but you might need to change the architecture and use a state management tool to achieve greater things.
Parent Widget class:
class MyParentWidget extends StatelessWidget {
const MyParentWidget({Key? key}) : super(key: key);
#override
Widget build(BuildContext context) {
return NotificationListener<FocusNotification>(
onNotification: (notification) {
print("New widget focused: ${notification.childKey.toString()}");
return true;
},
child: Row(
children: List.generate(
5,
(index) => MyChildWidget(
Key('widget-$index'),
),
),
),
);
}
}
Child Widget class:
class MyChildWidget extends StatefulWidget {
const MyChildWidget(Key key) : super(key: key);
#override
_MyChildWidgetState createState() => _MyChildWidgetState();
}
class _MyChildWidgetState extends State<MyChildWidget> {
final node = FocusNode();
#override
initState() {
node.addListener(() {
if (node.hasFocus) {
final notification = FocusNotification(widget.key!);
notification.dispatch(context);
}
});
super.initState();
}
#override
dispose() {
node.dispose();
super.dispose();
}
#override
Widget build(BuildContext context) {
return TextField(
focusNode: node,
);
}
}
Custom Notification class:
class FocusNotification extends Notification {
const FocusNotification(this.childKey);
final Key childKey;
}