Validation 如果我调用'；设置状态'；在'；onChange'；文本字段的

我有两个文本字段，电子邮件和密码。输入电子邮件后，用户进入密码字段，我显示默认消息“密码不得为空” 下面是密码文本字段小部件。我想在用户开始键入密码时隐藏此消息

注意：我必须使用Textfield小部件。 代码如下：

@override
Widget build(BuildContext context) {
final TextEditingController emailController =
    new TextEditingController(text: this._email);
final TextEditingController passwordController =
    new TextEditingController();

final submit = () async {
  try {
    FauiUser user = await fauiSignInUser(
      apiKey: this.widget.firebaseApiKey,
      email: emailController.text,
      password: passwordController.text,
    );
  } catch (e) {
    this.setState(() {
      this._error = FauiError.exceptionToUiMessage(e);
      //after typing email, when user presses <enter> or clicks in the Password field, the default message "Password must not be empty"
      //is assigned to this._error and displayed below Password Textfield widget
      this._email = emailController.text;
    });
  }
};

return Column(
    children: <Widget>[
      TextField(
        controller: emailController,
        autofocus: true,
        decoration: InputDecoration(
          labelText: 'EMail',
        ),
        onSubmitted: (s) {
          submit();
        },
      ),
      TextField(
        controller: passwordController,
        obscureText: true,
        decoration: InputDecoration(
          labelText: 'Password',
        ),
        onSubmitted: (s) {
          submit();
        },
      ),
      RaisedButton(
        child: Text('Sign In'),
        onPressed: submit,
      ),
    ]);

这将重建屏幕，消息将消失，但passwordController.text将被初始化，并且重建前输入的第一个字符将在该过程中丢失（例如，如果用户键入“hello”，则该值将变为“ello”）。 如何修复代码，使第一个字母不丢失？

试试这个

     TextField(
        controller: passwordController,
        obscureText: true,
        decoration: InputDecoration(
          labelText: 'Password',
          hintText: 'Password must not be empty'
        ),);

---

我意识到通过使用Focus，我可以获得类似的结果：

            child: TextField(
              controller: passwordController,
              obscureText: true,
              decoration: InputDecoration(
                labelText:"Password",
              ),
              onSubmitted: (s) {
                submit();
              },
            ),
            onFocusChange: (hasFocus) {
              if (hasFocus) {
                if (this._error.isNotEmpty) {
                  setState(() {
                    this._error = "";
                  });
                }}
            }),```

            child: TextField(
              controller: passwordController,
              obscureText: true,
              decoration: InputDecoration(
                labelText:"Password",
              ),
              onSubmitted: (s) {
                submit();
              },
            ),
            onFocusChange: (hasFocus) {
              if (hasFocus) {
                if (this._error.isNotEmpty) {
                  setState(() {
                    this._error = "";
                  });
                }}
            }),```