Ensuring numeric input
Michael J. Lew
michaell at unimelb.edu.au
Wed Oct 26 20:34:45 EDT 2005
How can I prevent users from being able to make non-number values in
a field? Simply preventing non-numeric keys is not enough because I
need to prevent things that use characters that are in valid numbers
to make non-numbers like 1.2.3 or -1.2-3.
I thought it would be relatively easy, but it might not be. Here is
the field script of a surprisingly complicated attempt:
on keydown thekey
if theKey is in "0123456789-." then --may be an allowable input
-- but I still need to check whether the result would be a valid number.
put value(the selectedLine) into thisLine --current number
put length(thisLine) into thisLineLen
put the selectedCHunk into sc --returns character locations from
start of field
--Need to find where the current line starts
put offset(thisLine,me,min(0,word 2 of sc-thislinelen)) into thisLineStart
--The characters to skip bit is an attempt to prevent the offset function
-- from returning a match to an earlier line in the field.
-- It needs the min function to prevent negative values.
--Now see if the input would make a non-numeric result
--First find where the selection point is in the line
put word 2 of sc +1 - thisLineStart into theSelectionStartChar
put word 4 of sc +1 - thisLineStart into theSelectionEndChar
--I don't know why I had to add one to the values...
put thisLineStart & return & theSelectionStartChar && theSelectionEndCHar
--Now test the input in the relevant place
put theKey into char theSelectionStartChar to theSelectionEndChar
--next line to help debugging
--put thisLine & return & thisLineStart & return &
theSelectionStartChar && theSelectionEndChar
if thisLine & "0" is a number then --should be OK
--Needs the appended zero to allow a line to start with a decimal point.
It seems to work, but it's an extraordinarily long and winding road
to get to a simple end-point. What am I missing?
Michael J. Lew
Department of Pharmacology
The University of Melbourne
Parkville 3010 put "-1" is a number
Phone +613 8344 8304
New email address: michaell at unimelb.edu.au
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