On 23 Sep 2011, at 6:48 PM, Philip McIntosh wrote:
> I have a calculation project using buttons to input numbers into a UILabel. I
> want it to format the numbers as they are entered to display grouping
> separators. It has been a struggle but so far the best I have ben able to
> achieve is this (I got the basic idea from a post at stackoverflow.com):
A threshold question: Do I understand correctly that the only record you have
of the value of your accumulator is the text contents of a label? Why? When you
call
> NSDecimalNumber *number = [NSDecimalNumber
> decimalNumberWithString:currentText];
you have no control at all over how the label's text is converted to a decimal.
It may or may not be lossy. Better that you keep, as a model object, the
decimal value, and avoid repeated round trips through the default parser. (You
are careful to specify U.S. grouping and decimal separators for _output_, but
the convenience parser you're using will use the separators from the current
locale.)
The rule is that you never, ever keep program state in a display object. If you
_must_ go through a string (which should still be a model object, and not
simply be left lying around in a label), set up an NSNumberFormatter and
setGeneratesDecimalNumbers:YES, so you can get some control. You can then keep
the formatter in a static variable, and reuse it for repeated conversions in
both directions — the round trip will be likelier to preserve your intended
value.
I'm also curious to know what you intend by
> currentText = [currentText stringByReplacingOccurrencesOfString:@"."
> withString:@"."];
Once you've tamed those issues, see if your
— F
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