unexpected message passing

Peter Brigham pmbrig at gmail.com
Sat Jul 28 00:02:07 EDT 2007


Here's a mystery -- to me, at any rate.

In one of my stacks I have a button that changes its function when  
clicked with the optionkey down. To alert the user, I have  
mouseEnter, mouseLeave, and mouseMove handlers in the button script  
that change the label of the button accordingly. At some point I  
noticed that the button label stayed changed after option-clicking it  
-- the first thing that happens is an answer dialog, so the user  
moves the cursor off the button to deal with that, leaving the button  
label in changed mode. I could have made sure to change it back in  
the button script, but instead I put a mousemove handler in the stack  
script, so that the button would revert to the primary label whenever  
the mouse was outside the button.

But then whenever I moved the cursor into the button with the  
optionkey down I'd get a rapid flicker between the two labels. I  
couldn't for the life of me figure out what was going on, as I do  
*not* have a pass mousemove command in the button script. BUT -- when  
I either comment out the stack mousemove script or put an empty  
blocking mousemove handler in the card script, the flickering stops.  
It looks as if the mousemove message is getting passed along the  
message hierarchy despite the lack of a "pass" command. How can this be?

I don't have duplicate mousemove handlers in button and stack scripts  
-- I checked. I have no relevant frontscripts and I'm using no extra  
stacks/libraries. The button is part of a group with  
backgroundbehavior set to true (so new cards inherit all controls),  
but there's nothing in the group script. It's a simple set-up in  
terms of the message path -- or it should be: button -> card -> group  
-> stack, except the button handler should block everything higher --  
and indeed, I can block it with an empty mousemove handler at the  
card level. I looked at the message watcher with mousemove messages  
unsuppressed, and every time I moved the mouse one pixel inside the  
button rect with the optionkey down the label changes briefly to the  
base state then back to the altered state, and I got *two* mousemove  
messages: one "mousemove" and one "mouseMove" -- note the capital M.  
I guess I don't understand this either. Why two? Does this confirm  
the unwarranted passing of the message?

I just tried creating a new empty stack with one button and mousemove  
handlers in the button and the stack scripts similar to those  
described above, but it doesn't flicker in that simple test stack. I  
don't know why it would do so in mine.

I can fix this easily in several ways, but I don't understand what is  
doing on.

Using Studio 2.8.1 build 471 on a Mac iBook G4 with OSX 10.4

-- Peter

Peter M. Brigham
pmbrig at comcast.net
http://home.comcast.net/~pmbrig/

-- PROGRAM, n. A spell cast over a computer allowing
     it to turn one's input into error messages.



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