Body of the input page which is non functional at the moment

nonfunctional_inputpage.dart

class InputPage extends StatefulWidget {
  @override
  _InputPageState createState() => _InputPageState();
}

class _InputPageState extends State<InputPage> {
  // Initialise isError bool variable to false. Used to change style of TextField widget if the user enters a value which isn't allowed.
  bool _isError = false;

  @override
  Widget build(BuildContext context) {
    return Container(
      margin: EdgeInsets.symmetric(vertical: 16, horizontal: 22),
      // Column because the TextField widget and button widget will be displayed vertically
      child: Column(
        // Want the widgets in the column to be displayed in the center
        mainAxisAlignment: MainAxisAlignment.center,
        children: <Widget>[
          // Widget needed to accept Text input from a user
          TextField(
            // User will only be inputting numbers so we want to make this easier for the user
            keyboardType: TextInputType.number,
            // No ones MMR is more than 4 digits long
            maxLength: 4,
            maxLengthEnforced: true,
            // How the TextField is styled
            decoration: InputDecoration(
                labelText: 'What\'s your MMR?',
                errorText:
                    _isError ? 'Enter a number between 0 and 9999' : null,
                border: OutlineInputBorder(
                  borderRadius: BorderRadius.all(Radius.circular(10)),
                )),
          ),
          // Creating space between the TextField widget and RaisedButton widget
          SizedBox(
            height: 20,
          ),
          // Putting RaisedButton widget inside a SizedBox so that I can change the size of the Raised button
          SizedBox(
            // Sets the width to as wide as possible. Parent widget has a margin which is why it doesn't go to the edge
            width: double.infinity,
            // RaisedButton widget. Currently disabled because onPressed property is null
            child: RaisedButton(
              onPressed: null,
              child: Text('SUBMIT'),
            ),
          ),
        ],
      ),
    );
  }
}