uevent(3tcl) User events uevent(3tcl)
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NAME
uevent - User events
SYNOPSIS
package require Tcl 8.4
package require uevent ?0.2?
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
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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 wid-
gets. 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 three commands, as specified below:
::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 gener-
ator 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 sys-
tem 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.
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 SF Trackers [http://sourceforge.net/tracker/?group_id=12883]. 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 Andreas Kupries <andreas_kupries@users.sourceforge.net>
uev 0.2 uevent(3tcl)