Path: utzoo!utgpu!water!watmath!clyde!att!osu-cis!tut.cis.ohio-state.edu!mailrus!ames!oliveb!felix!dhw68k!thecloud
From: thecloud@dhw68k.cts.com (Ken McLeod)
Newsgroups: comp.sys.mac.programmer
Subject: Re: Odd scrollbar behavior with TrackControl
Message-ID: <13726@dhw68k.cts.com>
Date: 24 Oct 88 10:02:28 GMT
References: <942@ccnysci.UUCP>
Reply-To: thecloud@dhw68k.cts.com (Ken McLeod)
Organization: Wolfskill residence; Anaheim, CA (USA)
Lines: 50

In article <942@ccnysci.UUCP> alexis@ccnysci.UUCP (Alexis Rosen) writes:
>Then I wrote this bit of code to handle thumb dragging (before I did the
>ActionProc for the scroll arrows):
>WHILE iNo <> 1 DO BEGIN
> ModalDialog(NIL, iNo);
> IF iNo = 2 THEN BEGIN
>   TEScroll(0, -tx^^.lineHeight * (GetCtlValue(ControlHandle(item)) - pos),tx);
>   pos := GetCtlValue(ControlHandle(item))
>   END
> END
>
>What did bother me was the crash I kept getting when I defined an ActionProc
>for the scrollbar control. I said:
>  SetCtlAction(ControlHandle(item), @Scroller);
>just before starting the ModalDialog loop. Scroller is a procedure that handles
>clicks in the arrows and grey regions. The wierd thing is that the ActionProc
>worked just fine. It did everything it was supposd to. BUT- now, the instant
>I clicked on the thumb, the machine would crash. The debugger showed me that
>when I was clicking in the thumb, my ActionProc was passed a bad ControlHandle.
>Clicks elsewhere passed the correct handle.

  I had this happen to me also, using LSP 1.11a, when converting some code
that had worked just fine in the old System 3.2 days. In my case, I hadn't
declared my actionProc to have any arguments! Oops.

  You didn't post your "Scroller" procedure, so my guess is this: your
actionProc needs to declare its arguments (see IM vol 1 p 324).

PROCEDURE Scroller(theControl:ControlHandle; partCode:integer);
BEGIN
  {handle text scrolling}
END;

 rather than

PROCEDURE Scroller;
BEGIN
END; {wrong!}

 If the arguments aren't declared, you'll get garbage instead of the
correct ControlHandle.
 
 Hope this was helpful...


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