Can't find the cause of this error

Question

I am working through a Drupal 8 module building exercise from YouTube and I am not able to figure out what is causing an error. The relevant page loads and displays the form, but I get the following error message.

Notice: Trying to get property of non-object in Drupal\rsvplist\Form\RSVPForm->buildForm() (line 29 of modules/custom/rsvplist/src/Form/RSVPForm.php).
Drupal\rsvplist\Form\RSVPForm->buildForm(Array, Object) call_user_func_array(Array, Array) (Line: 518)
Drupal\Core\Form\FormBuilder->retrieveForm('rsvplist_email_form', Object) (Line: 275)
Drupal\Core\Form\FormBuilder->buildForm('rsvplist_email_form', Object) (Line: 93)
Drupal\Core\Controller\FormController->getContentResult(Object, Object) call_user_func_array(Array, Array) (Line: 123)
Drupal\Core\EventSubscriber\EarlyRenderingControllerWrapperSubscriber->Drupal\Core\EventSubscriber{closure}() (Line: 582)
Drupal\Core\Render\Renderer->executeInRenderContext(Object, Object) (Line: 124)
Drupal\Core\EventSubscriber\EarlyRenderingControllerWrapperSubscriber->wrapControllerExecutionInRenderContext(Array, Array) (Line: 97)
Drupal\Core\EventSubscriber\EarlyRenderingControllerWrapperSubscriber->Drupal\Core\EventSubscriber{closure}() (Line: 151)
Symfony\Component\HttpKernel\HttpKernel->handleRaw(Object, 1) (Line: 68)
Symfony\Component\HttpKernel\HttpKernel->handle(Object, 1, 1) (Line: 57)
Drupal\Core\StackMiddleware\Session->handle(Object, 1, 1) (Line: 47)
Drupal\Core\StackMiddleware\KernelPreHandle->handle(Object, 1, 1) (Line: 99)
Drupal\page_cache\StackMiddleware\PageCache->pass(Object, 1, 1) (Line: 78)
Drupal\page_cache\StackMiddleware\PageCache->handle(Object, 1, 1) (Line: 47)
Drupal\Core\StackMiddleware\ReverseProxyMiddleware->handle(Object, 1, 1) (Line: 38)
Drupal\webprofiler\StackMiddleware\WebprofilerMiddleware->handle(Object, 1, 1) (Line: 52)
Drupal\Core\StackMiddleware\NegotiationMiddleware->handle(Object, 1, 1) (Line: 23)
Stack\StackedHttpKernel->handle(Object, 1, 1) (Line: 693)
Drupal\Core\DrupalKernel->handle(Object) (Line: 19)

The code for the form is the following.

/**
 *@file
 *Contains \Drupal\rsvplist\Form\RSVPForm
 */
namespace Drupal\rsvplist\Form;

use Drupal\Core\Database\Database;
use Drupal\Core\Form\FormBase;
use Drupal\Core\Form\FormStateInterface;

/**
 * Provides an RSVP email form
 */
class RSVPForm extends FormBase {

  /**
   * (@inheritdoc)
   */
  public function getFormId() {
    return 'rsvplist_email_form';
  }
  
  /**
   * (@inheritdoc)
   */
  public function buildForm(array $form, FormStateInterface $form_state) {
    $node = \Drupal::routeMatch()->getParameter('node');
    $nid = $node->nid->value;
    $form['email'] = array(
      '#title' => t('email address'),
      '#type' => 'textfield',
      '#size' => 25,
      '#description' => t("We will send updates to the email address you provide"),
      '#required' => TRUE,
    );

    $form['submit'] = array(
      '#type' => 'submit',
      '#value' => t('RSVP'),         
    );

    $form['nid'] = array(
      '#type' => 'hidden',
      '#value' => $nid,
    );

    return $form;
  }

  public function submitForm(array &$form, FormStateInterface $form_state) {
    drupal_set_message(t('The form is working'));
  }

}

I am using Drupal 8.6.15 which runs on PHP 7.0.15.

Can anyone spot an error I am missing?

Answer 1

Line line 29:

$nid = $node->nid->value;

Try this solution:

$node->id();

Very useful thing "Drupal 8 Entity API cheat sheet": https://www.metaltoad.com/blog/drupal-8-entity-api-cheat-sheet

Answer 2

Someone else had the same problem - this is the reason:

"In the video the form shows the form with no warnings, but when I try it shows the following warning: Notice: Trying to get property 'nid' of non-object in Drupal\rsvplist\Form\RSVPForm->buildForm()

This is caused by getting $node = \Drupal::routeMatch()->getParameter('node'); in a page with any node. So it returns NULL and fails trying to get the nid from NULL.

So the code should be updated to provide a default nid when $node is NULL. I guess this form will be displayed just on node pages, so the route /rsvplist will not be used. So keep watching the videos."

Answer 3

Here is what you should add to your code to avoid the error you have when you're not on a node page (I have improved as well to the latest standards, you might have to adjust since you're using D8 and PHP7) :

$node = \Drupal::routeMatch()->getParameter('node');
$nid = 0;
if ($node instanceof NodeInterface) {
  $nid = $node->id();  
}

Full code below :

<?php

/**
 *@file
 *Contains \Drupal\rsvplist\Form\RSVPForm
 */
namespace Drupal\rsvplist\Form;

use Drupal\Core\Form\FormBase;
use Drupal\Core\Form\FormStateInterface;
use Drupal\Core\StringTranslation\StringTranslationTrait;
use Drupal\node\NodeInterface;

/**
 *Provides an RSVP email form
 */

class RSVPForm extends FormBase {
  
  use StringTranslationTrait;
  
  /**
   * (@inheritdoc)
   */
  public function getFormId(): string {
    return 'rsvplist_email_form';
  }

  /**
   * (@inheritdoc)
   */
  public function buildForm(array $form, FormStateInterface $form_state): array {
    $node = \Drupal::routeMatch()->getParameter('node');
    $nid = 0;
    if ($node instanceof NodeInterface) {
      $nid = $node->id();  
    }
    $form['email'] = array(
      '#title' => $this->t('email address'),
      '#type' => 'textfield',
      '#size' => 25,
      '#description' => $this->t("We will send updates to the email address you provide"),
      '#required' => TRUE,
    );
    $form['submit'] = array(
      '#type' => 'submit',
      '#value' => $this->t('RSVP'),
    );
    $form['nid'] = array(
      '#type' => 'hidden',
      '#value' => $nid,
    );
    
    return $form;
  }
  
  public function submitForm(array &$form, FormStateInterface $form_state): void {
    $this->messenger()->addMessage($this->t('The form is working'));
  }
  
}