flutter - TextFormField 值消失以及如何获取 textFormField 值？

Question

请帮助解决我的 2 个问题。

第一个问题。为什么文本值消失？[已修复] @Praneeth我添加了动图 please click

我的代码就是这样用的

在我的小部件中，我调用了 UsernameTextField 类。小部件看起来像这样，

Widget build > WillPopScope > Scaffold > Form > ListView > children> Container (below container) I added key: _scaffoldKey, and key: formKey, also.

 Container(
                padding: EdgeInsets.all(16.0),
                margin: EdgeInsets.only(top: 30.0),
                child: UsernameTextField(),
              ),

用户名文本字段()

class UsernameTextField extends StatefulWidget{
  final usernameController = TextEditingController();
  @override
  State<StatefulWidget> createState() {
    return UsernameTextFieldState(usernameController);
  }
}

class UsernameTextFieldState extends State<UsernameTextField>{
  final usernameController;
  UsernameTextFieldState(this.usernameController);

  @override
  Widget build(BuildContext context) {
    return AppTextField(
        decoration: InputDecoration(
          contentPadding: const EdgeInsets.all(20.0),
          labelText: AppTranslations.of(context)
              .text("loginpage_username"),
        ),
        myController: usernameController,
        textInputType: TextInputType.emailAddress
    );
  }
}

AppTextField() 类，我将这个类用于我的每个 TextField 小部件

class AppTextField extends StatelessWidget {
  final InputDecoration decoration;
  final myController;
  final TextInputType textInputType;
  AppTextField({
    this.decoration,
    this.myController,
    this.textInputType
  });

  @override
  Widget build(BuildContext context) {
    return TextFormField(
        controller: myController,
        keyboardType: textInputType,
        textAlign: TextAlign.left,
        decoration: decoration
    );}}

第二个问题。如何获取textField的值？

在我调用的按钮onPressed()方法中，我调用了validation方法，但是结果是null

usernameValidation(){
  String username = UsernameTextField().usernameController.text;
  print(username);
} 

Answer 1

首先通过扩展为 StatefulWidget 而不是 StatelessWidget 将 UsernameTextField 类转换为 Stateful 类。然后你可以从 usernameController.text

获取值

更新

    class UsernameTextField extends StatefulWidget{
      final usernameController = TextEditingController();
      UsernameTextField(this.usernameController)

      @override
      State<StatefulWidget> createState() {
        return UsernameTextFieldState(usernameController);
      }
    }

    class UsernameTextFieldState extends State<UsernameTextField>{

      @override
      Widget build(BuildContext context) {
        return AppTextField(
            decoration: InputDecoration(
              contentPadding: const EdgeInsets.all(20.0),
              labelText: AppTranslations.of(context)
                  .text("loginpage_username"),
            ),
            myController: widget.usernameController,
            textInputType: TextInputType.emailAddress
        );
      }
    }