uevent(3tcl) 0.1.2 uev "User events"

NAME

uevent - User events

    TABLE OF CONTENTS
    SYNOPSIS
    DESCRIPTION
    API
    BUGS, IDEAS, FEEDBACK
    KEYWORDS
    COPYRIGHT

SYNOPSIS

package require Tcl 8.4
package require uevent ?0.1.2?
package require logger

::uevent::bind tag event command

command tag event details

::uevent::unbind token

::uevent::generate tag event ?details?

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:

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.
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.

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. Please also report any ideas for enhancements you may have for either package and/or documentation.

KEYWORDS

bind, event, generate event, unbind