How to default checkboxes to checked while maintaining custom return value

Question

I'm working on a migration project. I have a form in a custom module that creates a series of checkboxes for URLs to scrape. The form logic looks like this:

foreach ( \Drupal\scrape\Api\Scraper::loadUrls() as $index => $url ) {
  $form['url_' . $index] = [
    '#type' => 'checkbox',
    '#title' => $url . ' — ' . \Drupal::l('(link)', Url::fromUri($url)),
    '#return_value' => $url,
  ];
}

This code does what I want it to do, but all the checkboxes default to 'unchecked'.

'url_0' => integer0
'url_1' => string(27) "https://myurl1.com"
'url_2' => integer0

I want these checkboxes to default to checked. I couldn't find documentation on how to do it in Drupal 8, so I tried several things, and finally hit upon '#checked' => TRUE, (or any value that evaluates truthily). Now the checkboxes are defaulting to checked.

However, even though I have #return_value specified, the value returned in the form submission is now TRUE (from kint):

'url_0' => boolTRUE
'url_1' => boolTRUE
'url_2' => boolTRUE

Since any truthy value defaults the checkbox to checked, I tried '#value' => $url, but then upon submission, the values don't indicate their checked status:

'url_0' => string(86) "https://myurl0.com"
'url_1' => string(27) "https://myurl1.com"
'url_2' => string(29) "https://myurl2.com"

I guess my final option is to have a separate, hidden value for each URL, and map checkbox values to see if the user wants that URL included.

Is there a way I can default my checkboxes to TRUE, while maintaining their #return_value?

Answer 1

Sorry for such a late response but it is possible, I ran into this same issue using 8.5.3 the below configuration worked for me. You just have to use both together, i successfully passed numbers, text, bool (becomes 0 or 1), and arrays through #return_value. The class was just for formatting, you can leave that out if you're not using it.

'checkbox_1' => [
    '#type' => 'checkbox',
    '#title' => t('Checkbox 1'),
    '#default_value' => 1,         // Default to checked
    '#return_value' => "checked",  // Return the value if checked
    '#attributes' => ['class'=>['check_group']],
],
'checkbox_2' => [
    '#type' => 'checkbox',
    '#title' => t('Checkbox 2'),
    '#default_value' => 0,         // Default to unchecked
    '#return_value' => "checked",  // Return the value if checked
    '#attributes' => ['class'=>['check_group']],
],

Output will look like this if you dpm($form_state->getValues()) in your submit or validate function.

Array
(
    [checkbox_1] => checked
    [checkbox_2] => 0
)

Answer 2

You should use the #default_value property. E.g:

 $form['demo'] = [
    '#type' => 'checkbox',
    '#title' => $this->t('Demo'),
    '#default_value' => TRUE,
 ];

Answer 3

I guess you can't. I just created hidden fields, and mapped them in the submit.

This is what I basically did:

public function submitForm(array &$form, FormStateInterface $form_state) {

  $values = $form_state->getValues();

  $i = 0;

  while ( TRUE ) {
    if ( ! isset($values['checkboxes'][$i] ) {
      break;
    }
  }
}

That's not verbatim but basically what I did. Simple looping and checking for the checkbox value.