MacHack 1996/MacHack 1996.toast/Hacks/Hacks ’90/Validate Text Entry/Readme

Text File | 1990-06-15 | 3.1 KB | 55 lines | [TEXT/MPS ]

Validation of entry into Modal Dialogs

  I apologize for the fragmentary nature of this submission, but it is culled from some
Fortran code I happened to have with me, and as I do not have the Language Systems
Fortran compiler with me, and rewriting it in C was not something I had time to
do, it is submitted as is. There are some INCLUDE files I do not have with me, but
if there is serious interest in this hack, I will try to grind out a working demo
later. I cannot submit the entire program in which this feature exists, as there
is code in it which I did not write.

  The problem which this hack (and it is a hack, in every sense of the word) addresses
is how to solicit free text input from users and provide validation during entry.
The conditions this example covers are integers in a range, floating point in a range
(including the scientific format), and charater strings within a range of number of
characters. Also doable (but not done here) would be money, time, dates, etc.

  The approach is to attempt to reject an invalid key press when possible, i.e. if
the addition of that character to the string makes the string no longer meet the
SANE definition for representation of a floating point, don't add it to the string.
If the character is a valid character, but causes the string to exceed the bounds of
the specified format, add it to the string, but draw the string as greyed text and
grey the default round rect so the user understands that the value needs to be fixed
before proceeding. The user can see the validation criteria by pressing the option key.

  In order to do this, we need several components:

  1) NumValFilter, a ModalDialog filter proc which handles keyboard and mouse events
  2) ctlDimItem, a userItem which handles greying the text within the specified
     dialog item
  3) A Frm# resource, which specifies the validation criteria and the item in which
     to display the validation criteria. Note that due to the inability of Rez
     to generate a floating point number in a civilized fashion, I build this resource
     with the assembler. How embarrising for Apple...
  4) A routine which sets up the ModalDialog call

  As in any hack, there are areas in which this code battles nobly against the
operating system (and wins). Specifically, if the user selects several characters
and then presses a key, we need to carefully evaluate what the result will be,
lest we replace a valid number with a letter. Also, we need to clean up the field
if there was a selection range and the user tabs or clicks out of the field, as
the Dialog manager will try to redraw the field and ungrey the text.

  Since I wrote all this, I believe I know better ways to do what I am doing, and
may well rewrite this in C++, but I submit it mainly as an experiment in the human
interface which addresses a problem many of us face every day - how to avoid pissing
off the user by beeping and putting up an alert after the fact.

Jeff E Mandel MD MS
Asst Professor of Anesthesiology
1430 Tulane Ave
Tulane University School of Medicine
New Orleans, LA 70112

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