On 02/04/2009, at 12:17 PM, Greg Robertson wrote:
I would like to convert an NSString to an NSNumber. Is there a direct
method for this or should I go NSString to double and then double to
NSNumber?
One reason this isn't directly supported is probably because it only
has meaning within a very narrow scope. What is the numeric value of
"steve" for example? It hasn't got one of course. So you have to be
sure that your string does represent a number, which most strings do
not.
If you know your string contains a simple numeric constant (and only
this), the method others have pointed out will work.
Another class of strings do have meaningful numeric conversions also,
such as "3 + 4" or "sin(45)". If this is what you're interested in,
there is no built-in support for parsing this sort of string content,
but it can be done - for example check out:
http://apptree.net/parser.htm
If you're simply after accepting a numeric value input by the user,
using an NSTextField with a suitable formatter then requesting its -
doubleValue: will return an NSNumber. Using a formatter allows you to
validate the input before the value gets passed on to other code.
--Graham
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