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
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 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 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.
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>