WebSocketChannel becomes null when passed to a StatefulWidget's State class - flutter

Question

I have a simple client code in which I'm trying to pass the WebSocketChannel instance to an inner stateful widget, and for some reason when I try to run the code the app crushes and displays on the screen "Unexpected null value. See also: https://flutter.dev/docs/testing/errors". It would be greatly appreciated if someone could explain to me why this happens and how to fix it.
The code:
import 'package:flutter/material.dart';
import 'package:web_socket_channel/web_socket_channel.dart';
class TestWidget extends StatefulWidget {
final WebSocketChannel channel;
const TestWidget(this.channel);
#override
_TestWidgetState createState() => _TestWidgetState();
}
class _TestWidgetState extends State<TestWidget> {
String buttonText = '';
_TestWidgetState() {
widget.channel.stream.listen((data){
setState(() {buttonText = data;});
});
}
#override
Widget build(BuildContext context) {
return ElevatedButton(
onPressed: (){widget.channel.sink.add('hello');},
child: Text(buttonText)
);
}
}
class App extends StatelessWidget {
final WebSocketChannel channel = WebSocketChannel.connect(
Uri.parse('ws://localhost:8000/')
);
#override
Widget build(BuildContext context) {
return MaterialApp(home: Scaffold(body:
TestWidget(channel)
));
}
}
void main() {
runApp(App());
}
Thanks in advance for the help.

Answer 1

Any particular reason why you put
final WebSocketChannel channel = WebSocketChannel.connect(
Uri.parse('ws://localhost:8000/')
);
in App? Move this line code to TestStateWidget constructor. It's best practice u follow null safety method when try to access an object.