manipulate form variables before render()

Question

I have the following line of code in a user-profile-form.tpl.php which Drupal uses to render an input field in the user's edit profile page.

print render($form['field_machine_name']);
// this field can be found in the database table field_data_field_machine_name

The issue is that I want to run the value field_machine_name through a function like $form['field_machine_name'] = make_seo_url($form['field_machine_name']) before I run the render() function. But this totally breaks the form because $form['field_machine_name'] is some very large array and render() output html input tag instead of the actual field_machine_name itself.

How does one actually go about massaging values in the $form variable before outputting it as an html field in render()?

Additionally, i want to make sure anytime field_machine_name is printed anywhere on the drupal site, i want it to run through the make_seo_url() function. Is there a global place i can do this?

Answer 1

The Form API has #pre_render per element. You can use hook_form_alter to add your pre-render function to the list of functions that need to be called to show the value.

#pre_render

Used by: All elements and forms.

Description: Function(s) to call before rendering in drupal_render() has occured. The function(s) provided in #pre_render receive the element as an argument and must return the altered element.

Values: An array of function names to call.

Note: If you are altering an existing form via hook_form_alter() or a similar means, be careful with this property! As demonstrated here, you will probably want to add to the existing array rather than writing over it.

I recommend being careful of when your module runs when trying to interact with Forms, Ajax, etc (your modules' weight). If needed I also recommend seeing hook_module_implements_alter if you want to adjust when your hook is called, without affecting your modules' weight.

Answer 2

You need to hook into the form before processing the $form array not in a template file. See hook_form_alter. Also if you are wanting to make a field output a certain way when that field is rendered you need to look into changing the field template.

What you are doing is trying to render a form field inside a template which does not work.

Answer 3

You can do it in template_preprocess_field()

function mytheme_preprocess_field(&$variables, $hook) {
  $element = $variables['element'];
  if (isset($element['#field_name'])) {
    if ($element['#field_name'] == 'field_machine_name') {
          //do your changes
    }
  }
}

Answer 4

In the template.php of the appropriate theme, run code similar to the snippet i am giving:

function themename_form_user_profile_form_alter(&$form, &$form_state) {
  // dpm($form);
  // Use dpm to see the actual values that you are getting. Based on that change the lines below. Since $form is passed by refernce to this funciton, whatever change you make to the values, will be updated on the tpl file also.
  $old_value = $form['#user']->field_field_name['und'][0]['value'];
  $messaged_value = make_seo_url($old_value);
  $form['#user']->field_field_name['und'][0]['value'] = $messaged_value;
}

I think this should help. It uses hook_form_FORM_ID_alter(). To use dpm(), the Devel module needs to be enabled and the logged-in user needs to have the proper permissions to see the debug information.