---
name: "Prima::EventHook"
section: "3"
platform: "linux"
package: "libprima-perl"
version: "1.28-1.3+b3"
release: "Debian 8 (Jessie)"
platforms: ["linux"]
url: "https://new.carta.tech/Prima::EventHook"
---

# Prima::EventHook(3)

event filtering

## NAME

Prima::EventHook - event filtering

## SYNOPSIS

```
        use Prima::EventHook;
        sub hook
        {
                my ( $my_param, $object, $event, @params) = @_;
                ...
                print "Object $object received event $event\n";
                ...
                return 1;
        }
        Prima::EventHook::install( \&hook,
                param    => $my_param,
                object   => $my_window,
                event    => [qw(Size Move Destroy)],
                children => 1
        );
        Prima::EventHook::deinstall(\&hook);
```

## DESCRIPTION

Prima dispatches events by calling notifications registered on one or more objects interested in the events. Also, one  event hook can be installed that would receive all events occurred on all objects. `"Prima::EventHook"` provides multiplex access to the core event hook and introduces set of dispatching rules so  the user hook subs receive only a defined subset of events.

The filtering criteria are event names and object hierarchy.

## API

### install SUB, %RULES

Installs SUB into hook list using hash of RULES.

The SUB is called with variable list of parameters, formed so first passed parameters from `'param'` key ( see below ), then event source object, then event name, and finally parameters to the event. SUB must return an integer, either 0 or 1, to block or pass the event, respectively.  If 1 is returned, other hook subs are called; if 0 is returned, the event is efficiently blocked and no hooks are further called.

Rules can contain the following keys:

- event

  Event is either a string, an array of strings, or `"undef"` value.  In the latter case it is equal to `'*'` string, which selects all events to be passed in the SUB. A string is either name of an event, or one of pre-defined event groups,  declared in `%groups` package hash. The group names are:

  ```
          ability
          focus
          geometry
          keyboard
          menu
          mouse
          objects
          visibility
  ```

  These contain respective events. See source for detailed description.

  In case `'event'` key is an array of strings, each of the strings is also name of either an event or a group. In this case, if `'*'` string or event duplicate names are present in the list, SUB is called several times which is obviously inefficient.

- object

  A Prima object, or an array of Prima objects, or undef; the latter case matches all objects. If an object is defined, the SUB is called if event source is same as the object.

- children

  If 1, SUB is called using same rules as described in `'object'`, but also if the event source is a child of the object. Thus, selecting `"undef"` as a filter object and setting `'children'` to 0 is almost the same as selecting `$::application`, which is the root of Prima object hierarchy, as filter object with `'children'` set to 1.

  Setting together object to `"undef"` and children to 1 is inefficient.

- param

  A scalar or array of scalars passed as first parameters to SUB  whenever it is called.

### deinstall SUB

Removes the hook sub for the hook list.

## NOTES

`"Prima::EventHook"` by default automatically starts and stops Prima event hook mechanism when appropriate. If it is not desired, for example for your own event hook management, set `$auto_hook` to 0.

## AUTHOR

Dmitry Karasik, \<dmitry@karasik.eu.org\>.

## SEE ALSO

Prima, Prima::Object