Error: Call to a member function on a non-object using ChoiceType of Symfony component form

Question

我在 Defaultcontroller 中有 showUsersAction()-方法，它应该呈现一个表单，应该可以从列表中 select 用户，按 submit -按钮，然后重定向到显示用户项目的路由 /showItems/{userId}。

我知道使用 link 可以轻松做到这一点，但我想利用 ChoiceType:

首先，我从 Symfony documentation 中复制了一个 ChoiceType 的示例，并稍加改动：

/**
 * @Route("/showUsers", name="showUsers")
 */
public function showUsersAction(){
    $users = $this->getDoctrine()->getManager()->getRepository('AppBundle:User')->findAll();

    $form = $this->createFormBuilder()
        ->setMethod('POST')
        ->add('user', ChoiceType::class, [
            'choices' => $users,
            'choice_label' => function($user) {
                /** @var User $user */
                return strtoupper($user->getUsername());//here is the problem
            },
            'choice_attr' => function($user) {
                return ['class' => 'user_'.strtolower($user->getUsername())];
            },
        ])
        ->getForm();

    return $this->render('default/showUsers.html.twig', 
        array('users' => $users, 'form' => $form->createView()));
}

我确信 $users 给出了一个包含 class User 对象的数组。当我在浏览器中执行路由时，出现以下错误消息：

Error: Call to a member function getUsername() on a non-object 
in src\AppBundle\Controller\DefaultController.php at line 50

第 50 行是注释行 return strtoupper($user->getUsername());

问题是什么，我该如何解决？
在我通过提交按钮提交到同一路径后，如何获得 selected 用户？

编辑：（因为可能重复）我当然知道getUsername()这个方法是不能调用的，因为$user是一个非对象，应该和Symfony文档没有关系。所以我的问题与 Symfony 的特殊解决方案有关，它与 100 个错误相同的其他问题完全无关。

Answer 1

请改用 entity 类型。这里有一个link到documentation。它是 choice 类型的子类型，具有完全相同的功能，而且每个选项 returns 都是一个实体对象。

Answer 2

因为我在设置 entity 类型字段时也遇到了麻烦，所以我决定 post 我的整个 action 函数和 twig 文件的解决方案在这里:

action方法：

/**
 * @Route("/showUsers", name="showUsers")
 */
public function showUsersAction(Request $request){
    // gets array of all users in the database
    $users = $this->getDoctrine()->getManager()->getRepository('AppBundle:User')->findAll();

    $form = $this->createFormBuilder()
    ->setMethod('POST')
    ->add('users', EntityType::class, array(
        'class' => 'AppBundle:User',
        'choices' => $users,

        // This combination of 'expanded' and 'multiple' implements radio buttons
        'expanded' => true,
        'multiple' => false,    
        'choice_label' => function ($user) {
                return $user->__toString();
        }
    ))

    // Adds a submit button to the form. 
    // The 'attr' option adds a class to the html rendered form
    ->add('selected', SubmitType::class, array('label' => 'Show User Items', 'attr' => array('class' => 'button')))
    ->getForm();

    $form->handleRequest($request);

    if ($form->isSubmitted()  && $form->isValid()) {
        // gets the selected user
        $selectedUser = $form["users"]->getData();

        // redirects to route 'showItems' with the id of the selected user
        return $this->redirectToRoute('showItems', array('userId' => $selectedUser->getId()));
    }

    // renders 'default/showUsers.html.twig' with the form as an argument
    return $this->render('default/showUsers.html.twig', array('form' => $form->createView()));
}

twig 文件:

{# 
    // app/Resources/views/default/showUsers.html.twig

    Description:
    twig file that implements a form in which one of all users can get
    selected via radio button to show the items of the user after a click
    on the submit button.

    @author goulashsoup

 #}
{% extends 'base.html.twig' %}
{% block title %}Users{% endblock %}
{% block body %}
    <div class="users">
        {{ form_start(form) }}
            {% for user in form.users %}
                {{ form_widget(user) }}
                {{ form_label(user) }}
                <br>
            {% endfor %}
            <br>
        {{ form_end(form) }}
    </div>
{% endblock %}

Error: Call to a member function on a non-object using ChoiceType of Symfony component form

Error: Call to a member function on a non-object using ChoiceType of Symfony component form

php

forms

symfony-forms

symfony