Undefined index: theme in views_plugin->theme_functions()

So what row style (The "Show" setting in the view) are you using?

I'm also getting this error using the Format Show: Content | Teaser. I don't get the error when I use the Fields format.

I discovered this error when I changed the Format Show value from Fields to Content. I changed the views template file and was going to rescan the theme files. I get the error after opening the Theme: Information link.

Did you ever find the cause for the error?

I am attempting to follow the tutorial here for creating a row-plugin. Here is the example code:

function views_json_views_plugins() {
  return array(
    'row' => array( //declare the unformatted row plugin
      'unformatted' => array(
        'title' => t('Unformatted'),
        'help' => t('(Displays the unformatted data for each row from the views query with each row on a new line. Set as | for views_json.'),
        'handler' => 'views_plugin_row_unformatted',
        'theme' => 'views_view_row_unformatted',
        'uses fields' => TRUE,
        'uses options' => TRUE,
        'type' => 'normal',
      )
     )  
  );
}

class views_plugin_row_unformatted extends views_plugin_row {
    
  function option_definition() {
    $options = parent::option_definition();
    $options['separator'] = array('default' => '|');
    return $options; // <-------------------- I added this line to the tutorial.  I believe it is required.  No?
  }

  /**
   * Provide a form for setting options.
   */
  function options_form(&$form, &$form_state) {
    $fields = $this->display->handler->get_option('fields');
    $options = array();
    foreach ($fields as $field => $info) {
      $handler = views_get_handler($info['table'], $info['field'], 'field');
      if ($handler) {
        $options[$field] = $handler->ui_name();
      }
    }
  
    $form['separator'] = array(
      '#title' => t('Separator'),
      '#type' => 'textfield',
      '#size' => 10,
      '#default_value' => isset($this->options['separator']) ? $this->options['separator'] : ',',
      '#description' => t('The separator is placed between fields.'),
    );
  }
  
}

I created a view, and under 'format', I set 'show' to 'Unformatted'.
When I attempt to display my view, I get the following error:

Notice: Undefined index: theme in views_plugin->theme_functions() (line 529 of /mysite/sites/all/modules/views/includes/plugins.inc).

Does anyone know what may be causing this problem?

Thanks very much
Mindy

P.S. I tried deleting the following code from function options_form(), but that did not resolve the problem:

    $fields = $this->display->handler->get_option('fields');
    $options = array();
    foreach ($fields as $field => $info) {
      $handler = views_get_handler($info['table'], $info['field'], 'field');
      if ($handler) {
        $options[$field] = $handler->ui_name();
      }
    }

Never mind. My mistake. I had commented out this 'theme' line in hook_views_plugins(), in an earlier attempt to debug a different problem:

'theme' => 'views_view_row_unformatted',

The "undefined index" error message went away when I uncommented this line.

I don't believe my resolution sheds any light on the problem others are having, so I am leaving this issue "active".

I get this error as well, and a defective pager for one of my views using

Show:Content | Full content

FILTER CRITERIA
Content: Published (Yes)
Content: Type (= Lost And Found)
(flag) Flags: Flagged (False/True/No Option)

SORT CRITERIA
Content: Post date (asc/desc) 

RELATIONSHIPS
Flags: found (by any user)

See #1491082: Undefined index: theme in theme_functions() (line 512 of views/includes/plugins.inc).