[REBOL] Re: Sticky Button Down State
From: SunandaDH::aol::com at: 30-Jun-2003 14:43
Daril:
> The sticky button is not very disirable to see, but
> even less, if user clicks button during wait, the
> events held in queue and then processed. Returning
> button immediately to "up" state is desireable but
> invites user clicks.
You have several "real world" issues here and, as usual, they complicate code
that looks very simple until you start adding the stuff to handle them.
As I see it, you have four main issues:
1. How to stop a block of code being executed a number of times concurrently
if someone repeatedly presses the button. This is important as REBOL can
crash if someone tries this;
2. How to allow the user to cancel a long-running operation;
3. How to change a button state to show "in-progess" or some such;
4. How to show a progress bar.
The last two are relatively trivial, so I'll leave them up to you. The first
two need some extra code. In the rewrite of your code below, I've added:
-- two extra "state variables" so we can track if a process is underway, and
we can request a termination;
-- A cancel button so the user can request the termination;
-- wait 0 in the action loop -- important as otherwise the cancel action will
be deferred until the main process is complete -- not what you want.
=====
Cancel-requested: false
in-process: false
sites: [
http://www.rebol.com
http://www.rebol.org
http://www.reboltech.com
http://www.rebolforces.com
]
unview/all
view layout [
button "Start Scan" [
if in-process [return true]
in-process: true
cancel-requested: false
foreach site sites [
wait 0
if cancel-requested [in-process: false
return true]
print read site
] ;; for
in-process: false
] ;; action
button "Cancel" red [
cancel-requested: true
] ;; action
] ;; layout
=====
[In the real, real world, you'd want to surround some of this with a 'try
block so that the extra variables get set correctly in the event of an error --
otherwise, higher level recovery and restart code may leave the variables
incorrectly set....If in-process
is accidentally left true for any reason, the button becomes effectively
disabled. Error-recover code can seem endless :-) ]
Sunanda
