access Controller.isEmpty from another widget

So, I have a textwidget in my main class and I made another class that contains a TextFormField. Depending if the textfield is empty, I would like to change the color of the text from my main class.

If I put the textfield in the same class as my text widget, I'm ale to access the controller to read out if the textfield is empty or not.

Now the problem is, when I put the textfield in a seperate class I don't manage to find a way to access that controller from my main class.

I struggle a lot with passing data to and from within Dart, so hopefully this will brighten my mind.

Works when in same class

child: Text(
       'This is a Text',
        style: TextStyle(
        color: txtFieldController.value.text.isEmpty? Colors.red : Colors.green,
        ),
),

I tried with "import '' as form"; and try to access it with form.textfieldClass().txtFieldcontroller, but that doesn't seem to work.

Solution

create a property for the controller in both classes, create the controller in the main class and then pass it to the form class.

class MainWidget extends StatelessWidget {
  // create controller
  final  txtFieldController = TextEditingController();

  // pass the controller to the other class \/
  final formWidget = FormWidget(txtFieldController: txtFieldController);

  // ...
}

class FormWidget extends StatelessWidget {
  // create controller
  final TextEditingController txtFieldController;

  // ...
}

full example code:
the form widget

class FormWidget extends StatelessWidget {
  // create a property for the controller \/
  final TextEditingController txtFieldController;

  const FormWidget({Key key, this.txtFieldController}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Center(
      child: TextFormField(
        controller: txtFieldController,
      ),
    );
  }
}

the Main widget

class MainWidget extends StatefulWidget {
  @override
  _MainWidgetState createState() => _MainWidgetState();
}

class _MainWidgetState extends State<MainWidget> {
  final txtFieldController = TextEditingController();

  @override
  void initState() {
    // updates the widget on changes
    // note, the docs say: 'Avoid calling setState() high up in the tree if the change is contained to a small part of the tree.'
    // but it's not a big deal in this case
    txtFieldController.addListener(() {
      setState(() {});
    });
    super.initState();
  }

  @override
  void dispose() {
    txtFieldController.dispose();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Center(
        child: Column(
          mainAxisSize: MainAxisSize.min,
          children: [
            Text(
              'This is a Text',
              style: TextStyle(
                color: txtFieldController.value.text.isEmpty ? Colors.red : Colors.green,
              ),
            ),
            // pass the controller to the other class \/
            FormWidget(txtFieldController: txtFieldController)
          ],
        ),
      ),
    );
  }
}