Default theme implementations

Functions and templates for the user interface to be implemented by themes.

Drupal's presentation layer is a pluggable system known as the theme layer. Each theme can take control over most of Drupal's output, and has complete control over the CSS.

Inside Drupal, the theme layer is utilized by the use of the theme() function, which is passed the name of a component (the theme hook) and an array of variables. For example, theme('table', array('header' => $header, 'rows' => $rows)); Additionally, the theme() function can take an array of theme hooks, which can be used to provide 'fallback' implementations to allow for more specific control of output. For example, the function: theme(array('table__foo', 'table'), $variables) would look to see if 'table__foo' is registered anywhere; if it is not, it would 'fall back' to the generic 'table' implementation. This can be used to attach specific theme functions to named objects, allowing the themer more control over specific types of output.

As of Drupal 6, every theme hook is required to be registered by the module that owns it, so that Drupal can tell what to do with it and to make it simple for themes to identify and override the behavior for these calls.

The theme hooks are registered via hook_theme(), which returns an array of arrays with information about the hook. It describes the arguments the function or template will need, and provides defaults for the template in case they are not filled in. If the default implementation is a function, by convention it is named theme_HOOK().

Each module should provide a default implementation for theme_hooks that it registers. This implementation may be either a function or a template; if it is a function it must be specified via hook_theme(). By convention, default implementations of theme hooks are named theme_HOOK. Default template implementations are stored in the module directory.

Drupal's default template renderer is a simple PHP parsing engine that includes the template and stores the output. Drupal's theme engines can provide alternate template engines, such as XTemplate, Smarty and PHPTal. The most common template engine is PHPTemplate (included with Drupal and implemented in phptemplate.engine, which uses Drupal's default template renderer.

In order to create theme-specific implementations of these hooks, themes can implement their own version of theme hooks, either as functions or templates. These implementations will be used instead of the default implementation. If using a pure .theme without an engine, the .theme is required to implement its own version of hook_theme() to tell Drupal what it is implementing; themes utilizing an engine will have their well-named theming functions automatically registered for them. While this can vary based upon the theme engine, the standard set by phptemplate is that theme functions should be named THEMENAME_HOOK. For example, for Drupal's default theme (Bartik) to implement the 'table' hook, the phptemplate.engine would find bartik_table().

The theme system is described and defined in theme.inc.

End of "defgroup themeable".

See also

theme()

hook_theme()

Hooks

Callbacks

File

modules/system/theme.api.php, line 3

Functions

Files