TextFormField值消失以及如何获得textFormField值？

Question

请帮我回答我的两个问题。

第一个问题。为什么文本值消失了？@Praneeth修正的我添加了gif 请点击

我用了我的代码，

在我的小部件中，我调用了UsernameTextField类。小部件看起来如下，

小部件构建> WillPopScope > Scaffold > Form > ListView > children>容器(容器下面)--我还添加了key: _scaffoldKey,和key: formKey,。

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

UsernameTextField()

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， --我在每个TextField Widget中都使用了这个类

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。如何获得textField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UsernameTextField类而不是StatelessWidget，将StatelessWidget类转换为重要类。然后你就可以从usernameController.text中得到价值

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
        );
      }
    }