How to tell the difference between multiple image_buttons on the same form?

Question

Using FormAPI to create a simple set of three image_buttons, in the form_submit handler there is no 'op' value set in $form_state and therefore no way to tell which image_button was clicked. Is this a limitation of image_buttons?

Here's what I used to create the form, and it's bare-bones submit handler that shows no information telling me which button was clicked:

function cex_dash_top_icons_block_form( $form_state ) {
  $form = array();
  global $base_url;  
  $projects_icon_path  = '/'.drupal_get_path('module','cex_dash').'/Projects-icon-med.jpg';
  $reporting_icon_path = '/'.drupal_get_path('module','cex_dash').'/Reporting-icon-med.jpg';
  $help_icon_path      = '/'.drupal_get_path('module','cex_dash').'/Help-icon-med.jpg';

  $form['projects'] = array(
    '#type'  => 'image_button',
    '#value' => 'Projects Dash',
    '#src'   => $projects_icon_path,
  );

  $form['reports']  = array(
    '#type'  => 'image_button',
    '#value' => 'Analytics Dash',
    '#src'   => $reporting_icon_path
  );

  $form['help']     = array(
    '#type'  => 'image_button',
    '#value' => 'Documentation Dash',
    '#src'   => $help_icon_path
  );

  return $form;
}

function cex_dash_top_icons_block_form_submit($form_id, &$form_state) {
  _devReport( 'cex_dash_top_icons_block_form_submit: form_state is "'.print_r($form_state,1).'"' );
}

And no matter which button is clicked, $form_state['values'] looks like this:

[values] => Array(
  [projects] => Projects Dash
  [reports] => Analytics Dash
  [help] => Documentation Dash
  [form_build_id] => form-b6c762d22d0fd2360d1804ef19043c7d
  [form_token] => 4f0ce5275cc923e8fb27c305b57bf414
  [form_id] => cex_dash_top_icons_block_form
)

Now, in the larger $form_state array there is a 'clicked_button' array, but that always only has the information for the last image_button.

Do I need to create one mini-form for each image_button?

Answer 1

This issue on drupal.org might help.

Answer 2

If you just need to know which button has been clicked to take the necessary action, then you should assign a different submission handler to each button; see Form buttons can define custom #submit and #validate handlers for more details.
Since Drupal 6, the 'op' element in the form values, corresponding to the button clicked when there are several in a form in Drupal 5.x, should no longer be relied upon and may not be present; see what reported in The 'op' element in the form values is deprecated and should not be relied upon.