Default value of a 'managed file' field

Question

I created an edit custom form (of a node) via a custom module. From this form, I have a "managed file" field (for one picture) and I set his default value to a fid; However, when my form is rendered, the "managed file" field doesn't show the image ratached. I don't understand why

My code :

$form['project']['image'] = array(
  '#type' => 'managed_file',
  '#title' => t('Image'),
  '#default_value' => 10, //Set 10 for the test, the fid "10" exist, I checked
);

My form rendered:

As you see, no image is loaded whereas the default_value is set to an existing fid (10)

Answer 1

For a managed file form element, #default_value is an array containing the file ID, as in the following code.

$form['project']['image'] = array(
  '#type' => 'managed_file',
  '#title' => t('Image'),
  '#default_value' => array(10),
);

Answer 2

In My case i needed to add default files to a multiple managed file field element in drupal 8. my filed name was "field_dpe_submission_file"

  $fids = [
      10,
      11,
      12,
    ];

function setDefaultsForFileField(array &$form, $fids) {
    $widget_clone = $form['field_dpe_submission_file']['widget'][0];
    $form['field_dpe_submission_file']['widget']['#file_upload_delta'] = count($fids);
    $form['field_dpe_submission_file']['widget']['#value'] = null;
    $form['field_dpe_submission_file']['widget']['#defaults_loaded'] = TRUE;
    foreach ($fids as $key => $value) {
      $value = (int) $value;
      $form['field_dpe_submission_file']['widget'][$key] = $widget_clone;
      $file_array = [
        'fids' => [
          $value,
        ],
        'display' => '1',
        'description' => '',
        'upload' => ''
      ];
      $form['field_dpe_submission_file']['widget'][$key]['#value'] = $file_array;
      $form['field_dpe_submission_file']['widget'][$key]['#default_value'] = $file_array;
      $form['field_dpe_submission_file']['widget'][$key]['#input'] = TRUE;
      $form['field_dpe_submission_file']['widget'][$key]['#delta'] = $key;
      $name = 'field_dpe_submission_file[' . $key . ']';
      $form['field_dpe_submission_file']['widget'][$key]['#name'] = $name;
      $form['field_dpe_submission_file']['widget'][$key]['#theme'] = 'file_managed_file';
      $form['field_dpe_submission_file']['widget'][$key]['#multiple'] = FALSE;
      $form['field_dpe_submission_file']['widget'][$key]['fids'] = [
        '#type' => 'hidden',
        '#value' => [
          $value,
        ],
        '#theme' => 'input__hidden'
      ];
    }
    // Add the default widget back in.
    $count = count($fids);
    $form['field_dpe_submission_file']['widget'][$count] = $widget_clone;
  }
?>

Answer 3

Simple settings form with Managed file field with default value:

Config file form:

public function buildForm(array $form, FormStateInterface $form_state) {
 $config = $this->config('bk.settings');

$form['static'] = [
  '#type' => 'details',
  '#title' => t('Static Files'),
  '#open' => TRUE,
];

$form['static']['upload'] = [
  '#type' => 'managed_file',
  '#title' => t('File Upload.'),
  '#progress_indicator' => 'bar',
  '#progress_message'   => t('Please wait...'),
  '#upload_location' => 'public://static',
  '#description' => 'Allowed formats: jpg img png svg woff woff2, File location: public://static',
  '#upload_validators'  => [
    'file_validate_extensions' => ['jpg img png svg woff woff2'],
  ],
  '#default_value' => $config->get('upload'),
  '#multiple' => TRUE,
]; 
}

Form Submit:

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

if ($file_id = $form_state->getValue(['upload', '0'])) {
  $file = File::load($file_id);
  $file->setPermanent();
  $file->save();
}

  $config = $this->config('bk.settings');
  $config->set('upload', $form_state->getValue('upload'));
  $config->save();  
}
}