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From: milne@ics.uci.edu (Alastair Milne)
Newsgroups: comp.sys.mac.programmer
Subject: Re: Who has hacked numeric TEdit?.
Message-ID: <16413@paris.ics.uci.edu>
Date: 2 Jun 89 02:54:16 GMT
References: <1076@mailrus.cc.umich.edu> <11722@well.UUCP>
Sender: news@paris.ics.uci.edu
Reply-To: Alastair Milne <milne@ics.uci.edu>
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Organization: Educational Technology Center, Dept. of ICS, UC Irvine
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odawa@well.UUCP (Michael Odawa) writes
>In article <1076@mailrus.cc.umich.edu> cash@csmil.umich.edu (Howard Cash) writes:
>> Who is willing to part with the code for an editable text item 
>> that only accepts valid numbers (real or integer)?
>
>You can intercept the keystrokes in the FilterProc you call with
>ModalDialog.  Then peek at every key event as it comes in.  If it's not
>a digit, change the event into a nullEvent and mark it as handled:

   I have a small problem with that approach: the user has no way of knowing
   why his keystrokes aren't registering.  There is nothing here to alert the
   user that only digits (and signs, and ".", etc.) are to be used.

   I think an alert is necessary for this, either right at the keystroke
   (perhaps the filterproc could show it, before turning the event into a
   null); but I don't know whether filterproc's are allowed to fire up alerts
   or dialogs.  The other way, of course, is simply to let the user finish and
   enter the text, then give the alert and restart the entry if the format is
   not completely numeric.  Advantages: simple slips of the finger are not
   rewarded with a whole alert, and the user gets the chance to edit and modfy
   as s/he sees fit.  

   Now for the nasty part.  I assuming we've been thinking so far about the
   entry of integers.  What about real numbers?  I may just have missed it, but
   I don't recall seeing any standards in I-M for real number format (beyond
   the settings of components that differ between countries.)  Having worked
   on CAI material for some years, where such entry has to be made very
   tolerant for students who've never used a computer before, I can attest the
   number of difficulties to consider.  Are there any standards for this?


   Alastair Milne