启用了表单表单按钮，字段验证后未更新

Question

我仍在学习Flutter，并为此挠头。我有一个包含3个字段的表格（电子邮件，密码和password_confirmation）。我正在使用验证器，并更新用作按钮启用状态的条件的变量。问题是，例如，我更改电子邮件时，按钮启用状态没有更新。如果我热重启，它将更新按钮状态。如何强制按钮重新评估其状况？Flutter这样做的方式是什么？谢谢

  bool _validEmail = false;
  bool _validPassword = false;
  bool _validPasswordConfirmation = false;
  bool _validAccount = false;
  SignUpError _serverSignUpErrors = null;


Form signup_form() {
return Form(
    key: _formKey,
    child: Column(
      crossAxisAlignment: CrossAxisAlignment.start,
      children: <Widget>[
        //Email field
        Container(
          margin: EdgeInsets.symmetric(vertical: 10),
          child: Column(
            crossAxisAlignment: CrossAxisAlignment.start,
            children: <Widget>[
              Text(
                "Email",
                style: TextStyle(fontWeight: FontWeight.bold, fontSize: 15),
              ),
              SizedBox(
                height: 10,
              ),
              TextFormField(
                  controller: _emailFieldController,
                  obscureText: false,
                  decoration: InputDecoration(
                      border: InputBorder.none,
                      fillColor: Color(0xfff3f3f4),
                      filled: true),
                  onChanged: (String value) {
                    if(_serverSignUpErrors?.email_errors?.isNotEmpty == true)
                      _serverSignUpErrors.email_errors.clear();
                  },
                  autovalidate: true,
                  validator: (value) {
                    _validEmail = false;
                    if (value.isEmpty)
                      return 'Please enter some text';
                    //Validate email
                    String p = r'^(([^<>()[\]\\.,;:\s@\"]+(\.[^<>()[\]\\.,;:\s@\"]+)*)|(\".+\"))@((\[[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\])|(([a-zA-Z\-0-9]+\.)+[a-zA-Z]{2,}))$';
                    RegExp regExp = new RegExp(p);
                    if(!regExp.hasMatch(value))
                      return 'Invalid email';
                    if(_serverSignUpErrors?.email_errors?.isNotEmpty == true)
                      return _serverSignUpErrors.email_errors.join(';');
                    _validEmail = true;
                    return null;
                  }
              )
            ],
          ),
        ),

        //Password field
        Container(
          margin: EdgeInsets.symmetric(vertical: 10),
          child: Column(
            crossAxisAlignment: CrossAxisAlignment.start,
            children: <Widget>[
              Text(
                "Password",
                style: TextStyle(fontWeight: FontWeight.bold, fontSize: 15),
              ),
              SizedBox(
                height: 10,
              ),
              TextFormField(
                  controller: _passwordController,
                  obscureText: true,
                  decoration: InputDecoration(
                      border: InputBorder.none,
                      fillColor: Color(0xfff3f3f4),
                      filled: true),
                  onChanged: (String value) {
                    if(_serverSignUpErrors?.password_errors?.isNotEmpty == true)
                      _serverSignUpErrors.password_errors.clear();
                    this.didChangeDependencies();
                  },
                  autovalidate: true,
                  validator: (value) {
                    _validPassword = false;
                    if (value.isEmpty || value.length < 4)
                      return 'Password must be at least 6 chars wide';
                    if(_serverSignUpErrors?.password_errors?.isNotEmpty == true)
                      return _serverSignUpErrors.password_errors.join(';');
                      _validPassword = true;
                    return null;
                  }
              )
            ],
          ),
        ),

        //Password field
        Container(
          margin: EdgeInsets.symmetric(vertical: 10),
          child: Column(
            crossAxisAlignment: CrossAxisAlignment.start,
            children: <Widget>[
              Text(
                "Password confirmation",
                style: TextStyle(fontWeight: FontWeight.bold, fontSize: 15),
              ),
              SizedBox(
                height: 10,
              ),
              TextFormField(
                  controller: _passwordConfirmationController,
                  obscureText: true,
                  decoration: InputDecoration(
                      border: InputBorder.none,
                      fillColor: Color(0xfff3f3f4),
                      filled: true),
                  onChanged: (String value) {
                    if(_serverSignUpErrors?.password_confirmation_errors?.isNotEmpty == true)
                      _serverSignUpErrors.password_confirmation_errors.clear();
                    this.didChangeDependencies();
                  },
                  autovalidate: true,
                  validator: (value) {
                    _validPasswordConfirmation = false;
                    if (value.isEmpty)
                      return 'Please enter password confirmation';
                    if(value != _passwordController.text)
                      return 'Password confirmation doesn\'t match password';
                    if(_serverSignUpErrors?.password_confirmation_errors?.isNotEmpty == true)
                      return _serverSignUpErrors.password_confirmation_errors.join(';');
                    _validPasswordConfirmation = true;
                    return null;
                  }
              )
            ],
          ),
        ),
        Center(
          child: FlatButton(
              onPressed: (_validEmail && _validPassword && _validPasswordConfirmation && _validAccount == false) ? () async => await onRegister() : null,
              disabledColor: Colors.blueGrey,
              child: Text(
                'Register Now',
                style: TextStyle(fontSize: 20, color: Colors.white),
              ),
              color: Colors.blue, //specify background color for the button here
              colorBrightness: Brightness.dark, //specify the color brightness here, either `Brightness.dark` for darl and `Brightness.light` for light
              highlightColor: Colors.red, //color when the button is being actively pressed, quickly fills the button and fades out after
              padding: EdgeInsets.symmetric(horizontal: 8.0, vertical: 5.0), // gives padding to the button
            ),
        ),
      ]
    )
  );

}

Answer 1

[看来您是== false正在颠倒您的预期行为。不确定这是否是您想要的。

onPressed: (_validEmail && _validPassword && _validPasswordConfirmation && _validAccount == false) ? () async => await onRegister() : null,

为了解决您的错误，您应该使用_validEmail，_validPassword等变量来包装要更改状态的所有内容。当您更改状态时，这将重新构建窗口小部件（包括按钮），以便在需要时启用它，并且您将获得想要的行为。