Flutter：在 android 模拟器中单击复选标记/输入按钮后，TextFormField 中的文本消失

Question

I have this flutter mobile application that I've been working on for a couple of days now..

I'v set up the login/register page and a dummy homepage and added authentication support.

I then noticed that some of my textformfields automatically delete the text inside when I click the checmark/enter button on the android emulator instance.

but the the text doesnt disapear whenever I click on anything else like another formfield or just the blank screen.

edit: it deletes the text from all my text form fields.

here is the code for one of the fields:

    final name_label = Text(
      '    First Name:',
      style: TextStyle(color: Colors.black54),
    );

    final name = TextFormField(
      validator: (val) {
        if (val == '') {
          return 'This Field Cannot Be Empty';
        } else if (val!.length > 20) {
          return "This Field Can't Have more than 20 characters";
        } else {
          return null;
        }
      },
      onFieldSubmitted: (value) {
        first_name_controller.text = value;
      },
      controller: first_name_controller,
      keyboardType: TextInputType.name,
      autofocus: false,
      decoration: InputDecoration(
        hintText: 'Joe',
        contentPadding: EdgeInsets.fromLTRB(20.0, 10.0, 20.0, 10.0),
        border: OutlineInputBorder(borderRadius: BorderRadius.circular(32.0)),
      ),
    );```  

Answer 1

made TextEditingController instances into class properties instead of instances at build time (build method).

class _LoginPageState extends State<LoginPage> {
  @override
  final AuthService _login_checker = AuthService();
  final _formkey = GlobalKey<FormState>();
  final login_email_controller = TextEditingController();
  final login_password_controller = TextEditingController();

  Widget build(BuildContext context) {
    final logo = Hero(
      tag: 'hero',
      child: CircleAvatar(
        backgroundColor: Color.fromARGB(0, 180, 32, 32),
        radius: 48.0,
        child: Image.asset(
            'lib/images/png-clipart-hamburger-button-computer-icons-marmon-keystone-canada-menu-red-sea.png'),
      ),
    );