On 23/04/2010, at 1:36 AM, Arnold Nefkens wrote:
> NSNumber *fieldOne = [managedObject valueForKey:@"key1"];
> NSNumber *fieldTwo = [managedObject valueForKey:@"key2"];
> NSNumber *fieldThree = [managedObject valueForKey:@"key3"];
> if (fieldTwo > 0) {
> NSNumber *answer = ((fieldTwo - fieldOne) + fieldThree);
> [self.managedObject setValue:[answer intValue] forKey:@"key4"];
> }
>
> If I debug the right values are being shown in the fieldOne, fieldTwo and
> fieldThree. But the calculation answer is all the time out of scope.....
>
> What am I missing?
NSNumbers are objects that CONTAIN the value to be added, subtracted, etc. They
cannot be added or subtracted directly.
You need to extract the value in the form you want it using methods such as
-floatValue, -intValue and so on before doing calculations. Unfortunately
perhaps, Obj-C does not allow operator overloading to allow direct use of
objects in math expressions.
--Graham
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