Callback function signatures.

Backdrop's API sometimes uses callback functions to allow you to define how some type of processing happens. A callback is a function with a defined signature, which you define in a module. Then you pass the function name as a parameter to a Backdrop API function or return it as part of a hook implementation return value, and your function is called at an appropriate time. For instance, when setting up batch processing you might need to provide a callback function for each processing step and/or a callback for when processing is finished; you would do that by defining these functions and passing their names into the batch setup function.

Callback function signatures, like hook definitions, are described by creating and documenting dummy functions in a *.api.php file; normally, the dummy callback function's name should start with "callback_", and you should document the parameters and return value and provide a sample function body. Then your API documentation can refer to this callback function in its documentation. A user of your API can usually name their callback function anything they want, although a standard name would be to replace "callback_" with the module name.

See also


Default theme implementations

Parent topics


core/includes/, line 659
API for loading and interacting with Backdrop modules.


Namesort descending Location Description
callback_batch_finished core/modules/system/form.api.php Complete a batch process.
callback_batch_operation core/modules/system/form.api.php Perform a single batch operation.
callback_filter_prepare core/modules/filter/filter.api.php Provide prepared text with special characters escaped.
callback_filter_process core/modules/filter/filter.api.php Provide text filtered to conform to the supplied format.
callback_filter_settings core/modules/filter/filter.api.php Provide a settings form for filter settings.
callback_filter_tips core/modules/filter/filter.api.php Return help text for a filter.
callback_search_conditions core/modules/search/search.api.php Provide search query conditions.
hook_ckeditor5_PLUGIN_plugin_check core/modules/ckeditor5/ckeditor5.api.php Enabled callback for hook_ckeditor5_plugins().
hook_ckeditor_PLUGIN_plugin_check core/modules/ckeditor/ckeditor.api.php Enabled callback for hook_ckeditor_plugins().
layout_route_handler core/modules/layout/layout.module Route handler callback; Execute the current route item or wrap in a layout.