Flutter - change TextFormField background when in active mode (Typing)

Question

I want to achieve this.

While a text form field is inactive, its background, fill color will be grey. But when I am typing or it is in active mode, its background color will be white.

How to achieve this behavior?

Answer 1

After going through some tests, I have finalized the correct answer. The above answer is good. The first one has a problem. Focus Node variable must be inside the state class so that it can preserve its state.

class _GlobalTextFormFieldState extends State<GlobalTextFormField> {
  late FocusNode focusNode;

  @override
  void initState() {
    focusNode = FocusNode();
    focusNode.addListener(() {
      setState(() {});
    });
    super.initState();
  }

  @override
  Widget build(BuildContext context) {
    return TextFormField(
      focusNode: focusNode,
    );
  }
}