[development] theming in D7

[Bob Hutchinson]

Hi folks, I'm struggling with theming in D7.

In D6 I can do the following:

create a form

function mymodule_thingy_form(&$form_state) {
  // build a form in the usual manner
  // .....
  return $form;
}

optionally create validate and submit functions

function mymodule_thingy_form_validate($form, &$form_state) {
  // validate form elements
}
function mymodule_thingy_form_submit($form, &$form_state) {
  // submit the form info etc
}

then I can render the form with
....
$output = drupal_get_form('mymodule_thingy_form');
return $output;
....

Now in order to control the rendering in a theme I can add an entry to the 
theme registry
function mymodule_theme() {
....
    'mymodule_thingy_form' => array(
      'arguments' => array(
        'form' => NULL,
      ),
    ),
....
}

and create a function
function theme_mymodule_thingy_form($form) {
  $output = drupal_render($form);
  return $output;
}

The form will be automatically fed through the theme function, providing the 
name is the same.

In D7 I get somewhat different behaviour:

If I do not create an entry in the theme registry, all works as expected, but 
if I do, things start to behave oddly.

function mymodule_theme() {
....
    'mymodule_thingy_form' => array(
      'variables' => array(
        'form' => NULL,
      ),
    ),
....
}
and create a function
function theme_mymodule_thingy_form($variables) {
  $form = $variables['form'];
  $output = drupal_render($form);
  return $output;
}

The form is not fed through the theme automatically and is not rendered at 
all, I see 'Array' where the form should be.

So I theme it explicitly with:
....
$form = drupal_get_form('mymodule_thingy_form');
$output = theme('mymodule_thingy_form', array('form' => $form));
return $output;
....

This results in no form visible at all, though there are mangled traces of it 
in the source html.
So I use dd($form) to find out what is going on and discover that it is going 
through the theme function twice and is being mangled on the second time 
through, so I modify the theme function.

function theme_mymodule_thingy_form($variables) {
  $form = $variables['form'];
  $output = (is_array($form) ? drupal_render($form) : $form);
  return $output;
}

Phew! my form is rendered.

This looks like a dreadful hack to me, what should I be doing?
Any pointers would be most welcome.

-- 
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Bob Hutchinson
Midwales dot com
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