Flutter Newbie: Modifying Textfield value breaks focus on TextField - flutter

Question

Go easy. I just started learning Flutter a week ago. I'm coming from ReactJS so I have a decent understanding of state management and lifecycle methods. But I'm completely new to Dart and Flutter and how it handles state.
I am writing a quick WebRTC chat application. I have a TextField I'm using to generate room names. I decided I wanted to make the labelText of the TextField, cycle through some random words, every 5 seconds, while the field is not in focus. If the field comes into focus, I stop cycling the label. I do this so that the field appears to have a pre generated random room name.
I am having trouble editing the TextField. I assume this is an issue with setState or my TextEditingController. I'm used to being able to access an input's value, so controllers are odd to me.
Here is my ChangingTextField:
import 'dart:async';
import 'package:english_words/english_words.dart';
import 'package:flutter/material.dart';
//
class ChangingTextField extends StatefulWidget {
final TextEditingController controller;
ChangingTextField({
Key? key,
required this.controller,
}) : super(key: key);
#override
_ChangingTextFieldState createState() => _ChangingTextFieldState();
}
class _ChangingTextFieldState extends State<ChangingTextField> {
FocusNode _focusNode = FocusNode();
Timer? _timer;
String _roomName = "example.com/";
bool _wasFocused = false;
#override
void initState() {
super.initState();
_focusNode = FocusNode();
_timer = Timer.periodic(Duration(seconds: 5), (Timer t) => _genRoomName());
}
#override
void dispose() {
_timer?.cancel();
_focusNode.dispose();
super.dispose();
}
void _requestFocus(){
if(!_wasFocused){
setState(() {
_timer?.cancel();
_wasFocused = true;
FocusScope.of(context).requestFocus(_focusNode);
});
}
}
void _genRoomName(){
WordPair wp = generateWordPairs().take(1).first;
setState(() => _roomName = "example.com/" + wp.first + "-" + wp.second );
}
#override
Widget build(BuildContext context) {
return Container(
child: TextField(
focusNode: _focusNode,
controller: widget.controller,
decoration: InputDecoration(
border: OutlineInputBorder(),
labelText: _wasFocused ? "example.com/" : _roomName,
),
onTap: _requestFocus,
),
);
}
}
The parent widget simply passes a TextEditingController into this widget so that I can listen for changes, and (I assume) gather the value of the TextField at a later point in time.
The listener is defined like this in the parent widget:
#override
void initState() {
roomNameController.addListener(() {
setState(() {});
});
super.initState();
}
However, every time I try to change the value of the TextField, after every character that I type, the focus is broken on the ChangingTextField widget, and I must click again inside the TextField to type my next character. I am assuming this issue is because the listener calls setState in the parent widget.
In React terminology I would refer to this as a re-render. If the parent re-renders, the child goes with it, and so the app loses what knowledge it had of where in the widget tree the user was working. However, I feel that the controller needs to exist in the parent, such that, I can acquire the value of the child when needed (e.g. on a button press). Lifting state up and whatnot.
Can someone explain to me what is going on here?

Answer 1

I found the solution. Listening inside of the widget instead of initializing the listener in the parent component, produces the behavior you would expect.
In short, moving the following code:
#override
void initState() {
roomNameController.addListener(() {
setState(() {});
});
super.initState();
}
into the ChangingTextField widget's initState as opposed to having it in the parent's initState, resolved the problem. Best of all, the controller is still created by the parent, so the controller's text is available in the parent when the submit button is pressed.