NetNews Usenet Archive 1992 #18/NN_1992_18.iso/spool/comp/lang/tcl/1205

Internet Message Format | 1992-08-17 | 2.8 KB

Path: sparky!uunet!sun-barr!ames!agate!sprite.Berkeley.EDU!ouster
From: [e-mail] (John Ousterhout)
Newsgroups: comp.lang.tcl
Subject: Re: Question on binding
Date: 17 Aug 1992 15:32:12 GMT
Organization: U.C. Berkeley Sprite Project
Lines: 49
Distribution: world
Message-ID: <[e-mail]>
References: <[e-mail]>
NNTP-Posting-Host: tyranny.berkeley.edu
Keywords: binding

Subject: Re: Question on binding
Keywords: binding

In article <[e-mail]>, [e-mail] (Te-Wei Sun) writes:
|>
|> Hi,
|>
|> I wrote a short script in tk trying to bind several mouse events for
|> canvas. The goal I am trying to achieve here is as follows:
|>
|> If I click button 1 once on the canvas, I would like to see the message
|> "b1 pressed once".
|>
|> If I double click button 1 on the canvas, I would like to see ONLY the
|> message "b1 pressed twice", not "b1 pressed once" and "b1 pressed twice",
|> The same applied for triple click.
|>
|> If I click button 1 on the rectangle widget, I would like to see ONLY the
|> message "b1 pressed once on rectangle", not "b1 pressed once" and "b1 pressed once on rectangle".
|>
|> If I double click button 1 on the rectangle widget, I would like to see ONLY
|> the message "b1 pressed twice on rectangle" and so on for triple click.
|>
|>
|> Is there any way I can achieve the way I would like to have my bindings?
|>

There are a couple of things to realize here.  First bindings on widgets
(e.g. "bind .c <1> ...") are independent of bindings on individual items or
tags within canvases (e.g. ".c bind 2 <1> ...").  If you set up a binding on
a rectangle within a canvas and also a separate binding on the canvas, both
will trigger when you click with the mouse in the rectangle.  It sounds like
you want a way to distinguish between a click over an item and a click when
the mouse isn't over any item.  You can distinguish these by checking to see
if there is a "current" item.  If the command ".c find withtag current"
returns an empty string then the mouse isn't over an item.  You can use this
in the binding for the whole canvas to do nothing when there is a current
item.

Second, you will always get a single-click event before a double-click event.
The reason for this is that at the time of the single-click event there's no
way to know whether or not a second click is going to follow, so Tk always
issues the single-click event.  If you don't want to process the single-click
in cases where there is (eventually) a double click, then use the "after"
command in your single-click event handler to delay the real work you want
to do for a while.  If a double-click event follows in the interim, then
you can cancel the real work.  This has the disadvantage of introducing a
delay in processing single clicks, but I don't see any alternative, given
your desires.