NSNumber sum

[mindus]

Hi

NSNumber start;
start = [NSNumber numberWithInt:([start intValue] + 5)];

i can able to increment up to three times (start = 16). After that if i try to increase this, i am getting Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '*** -[UILabel intValue]: unrecognized selector sent to instance 0x392be00'
exception

anybody know how to solve this

Thanks
mindus

[TUX2K]

It looks like that some how your object changes from NSNumber to UILabel.
Could you post a bit more code?

[Ice_2k]

try using NSNumber*

[ChrisL]

numberWithInt: returns an autoreleased NSNumber object. If you don't explicitly retain it, it will be deallocated when the autorelease pool is drained at the end of the current iteration of the run loop. When this happens, 'start' becomes a dangling pointer -- the object it points to no longer exists.

When an object is deallocated, the memory isn't necessarily replaced right away, so it's possible that subsequent messages sent will still work normally for a while. Eventually, though, the freed memory is reused for a new object -- in your case, the memory previously occupied by the NSNumber now contains a UILabel. The pointer 'start' now erroneously points to a UILabel, which doesn't know how to respond to the intValue message and throws the exception you're seeing.

So, you need to make sure to retain the NSNumber returned by the numberWithInt: method, and then release it once you no longer need it. The easiest way to do this is by creating and using a retained property; this will take care of the memory management for you. See Brian Slick's properties guide for an overview.

[Duncan C]

Originally Posted by mindus

Hi

NSNumber start;
start = [NSNumber numberWithInt[start intValue] + 5)];

i can able to increment up to three times (start = 16). After that if i try to increase this, i am getting Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '*** -[UILabel intValue]: unrecognized selector sent to instance 0x392be00'
exception

anybody know how to solve this

Thanks
mindus

The other poster told you what was wrong with your code. You need to retain the NSNumber you are creating, and release the old one before you replace it.

This would be a perfect application for using a retained property.

If you declare start as a retained property in your header, like this:

@property (nonatomic, retain) NSNumber* start;

and in the body of your class, synthesize it like this:

@synthesize start;

Then your code can read like this:

self.start = [NSNumber numberWithInt:([start intValue] + 5)];

Note that we are saving a value to start using property notation (self.start). That causes the code to call the setter for the start property, which retains the new value and releases the old value.