NAME¶
uevent - User events
SYNOPSIS¶
package require
Tcl 8.4
package require
uevent ?0.3.1?
package require
logger
::uevent::bind tag event command
command tag event details
::uevent::unbind token
::uevent::generate tag event ?
details?
::uevent::list
::uevent::list tag
::uevent::list tag event
::uevent::watch::tag::add pattern command
{*}command bound tag
{*}command unbound tag
::uevent::watch::tag::remove token
::uevent::watch::event::add tag_pattern event_pattern
command
{*}command bound tag event
{*}command unbound tag event
::uevent::watch::event::remove token
DESCRIPTION¶
This package provides a general facility for the handling of user events. Allows
the binding of arbitrary commands to arbitrary events on arbitrary tags,
removal of bindings, and event generation.
The main difference to the event system built into the Tcl/Tk core is that the
latter can generate only virtual events, and only for widgets. It is not
possible to use the builtin facilities to bind to events on arbitrary
(pseudo-)objects, nor is it able to generate events for such.
Here we can, by assuming that each object in question is represented by its own
tag. Which is possible as we allow arbitrary tags.
More differences:
- [1]
- The package uses only a two-level hierarchy, tags and events, to handle
everything, whereas the Tcl/Tk system uses three levels, i.e. objects,
tags, and events, with a n:m relationship between objects and tags.
- [2]
- This package triggers all bound commands for a tag/event combination, and
they are independent of each other. A bound command cannot force the event
processing core to abort the processing of command coming after it.
API¶
The package exports eight commands, as specified below. Note that when the
package is used from within Tcl 8.5+ all the higher commands are ensembles,
i.e. the :: separators can be replaceed by spaces.
- ::uevent::bind tag event command
- Using this command registers the command prefix to be triggered
when the event occurs for the tag. The result of the command
is an opaque token representing the binding. Note that if the same
combination of < tag,event,command> is used
multiple times the same token is returned by every call.
The signature of the command prefix is
- command tag event details
where
details contains the argument(s) of the event. Its contents are
event specific and have to be agreed upon between actual event generator and
consumer. This package simply transfers the information and does not perform
any processing beyond that.
- ::uevent::unbind token
- This command releases the event binding represented by the token.
The token has to be the result of a call to ::uevent::bind. The
result of the command is the empty string.
- ::uevent::generate tag event ?details?
- This command generates an event for the tag, triggering all
commands bound to that combination. The details argument is simply
passed unchanged to all event handlers. It is the responsibility of the
code generating and consuming the event to have an agreement about the
format and contents of the information carried therein. The result of the
command is the empty string.
Note that all bound commands are triggered, independently of each other. The
event handlers cannot assume a specific order. They are also not
called synchronously with the invokation of this command, but simply put
into the event queue for processing when the system returns to the event
loop.
Generating an event for an unknown tag, or for a <
tag,event> combination which has no commands bound to it
is allowed, such calls will be ignored.
- ::uevent::list
- In this form the command returns a list containing the names of all tags
which have events with commands bound to them.
- ::uevent::list tag
- In this format the command returns a list containing the names of all
events for the tag with commands bound to them. Specifying an
unknown tag, i.e. a tag without event and commands, will cause the command
to throw an error.
- ::uevent::list tag event
- In this format the command returns a list containing all commands bound to
the event for the tag. Specifying an unknown tag or unknown
event, will cause the command to throw an error.
- ::uevent::watch::tag::add pattern command
- This command sets up a sort of reverse events. Events generated, i.e. the
command prefix invoked, when observers bind to and unbind from
specific tags.
Note that the command prefix is only invoked twice per tag, first when the
first command is bound to any event of the tag, and second when the last
command bound to the tag is removed.
The signature of the command prefix is
- {*}command bound tag
- {*}command unbound tag
The result of the command is a token representing the watcher.
- ::uevent::watch::tag::remove token
- This command removes a watcher for (un)bind events on tags.
The result of the command is the empty string.
- ::uevent::watch::event::add tag_pattern event_pattern
command
- This command sets up a sort of reverse events. Events generated, i.e. the
command prefix invoked, when observers bind to and unbind from
specific combinations of tags and events.
Note that the command prefix is only invoked twice per tag/event
combination, first when the first command is bound to it, and second when
the last command bound to the it is removed.
The signature of the command prefix is
- {*}command bound tag event
- {*}command unbound tag event
The result of the command is a token representing the watcher.
- ::uevent::watch::event::remove token
- This command removes a watcher for (un)bind events on tag/event
combinations.
The result of the command is the empty string.
BUGS, IDEAS, FEEDBACK¶
This document, and the package it describes, will undoubtedly contain bugs and
other problems. Please report such in the category
uevent of the
Tcllib Trackers [
http://core.tcl.tk/tcllib/reportlist]. Please also
report any ideas for enhancements you may have for either package and/or
documentation.
SEE ALSO¶
hook(3tcl)
KEYWORDS¶
bind, event, generate event, hook, unbind
CATEGORY¶
Programming tools
COPYRIGHT¶
Copyright (c) 2007-2012 Andreas Kupries <andreas_kupries@users.sourceforge.net>