[[Explain virtual events.  Is there a tutorial?
Illustrate usage.  Put forward references in appropriate
places--what are those?  "advanced Tk-ing?"]]








[[Important thread:
http://groups.google.com/groups?th=5f799aadcb2caf35 ]]

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[Bryan Oakley]'s wizard mega- (meta?) widget taught me a ''wonderful'' use of virtual events.  Whereas I had code in my wizard implementation like:

    proc doNextThing { args } {
       ...
    }
    button $w.next -text "Next" -command doNextThing
    
Bryan had the foresight to indirect the button handling via virtual events.  Now I do something like:

    proc doNextThing { args } {
    }
    proc dispatch { event } {
        switch -- $event {
            <<Next>> {
                doNextThing
            } 
            ...
        }
    }
    ...
    button $w.next -text "Next" \
        -command [list event generate $w <<Next>>]
    bind $w <<Next>> [list dispatch <<Next>>]

The wonder of this is that my testing harness can do:

    bind $w <<Next>> {+doTestingThing}

and trap the button presses without making invasive changes to the wizard code!

--[Chris Nelson]

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[MC] (5 May 2003): Until today I hadn't realized that you could have Virtual Events that weren't associated with a real physical event.  Then while googling on [event] add I came across this[http://groups.google.com/groups?selm=u1tT9.47%24fF3.61480166%40newssvr11.news.prodigy.com] enlightening comp.lang.tcl post from [Bryan Oakley].