iOS @synthesize and semi complex objects (NSNumber)

[seepel]

I'm a bit new to Cocoa programming and I understand how @synthesize will work with C type variables, like ints and floats. If I try to use it with something like an NSNumber, however, I don't understand what it's doing. Can anyone shed some light on the issue?

 

[robbieduncan]

It depends somewhat on how you declare it (retain or assign for example). Regardless it's all covered in the documentation.

 

[seepel]

Thanks for the reference I'd been looking for a page like that. But I still don't quite understand, this is my conception.

If I use assign I would expect something like this

@property NSNumber *number

- (void)setNumber:(NSNumber*) n { number = n; }

and retain

@property (retain) NSNumber *number;

- (void)setNumber:(NSNumber*) n {
    [number release];
    number = n;
    [number retain];
}

and copy

@property (copy) NSNumber * number;

- (void)setNumber:(NSNumber*) n {
   number = [n copy];
}

At least with retain this isn't what I see. The number never seems to get set. So if I run this I get 0 back.

The class.

@interface SomeClass : NSObject {
    NSNumber *number;
};

@property (retain) NSNumber *number;
@end

@implementation SomeClass
@synthesize number;
@end

And the calling

[someClass setNumber:[NSNumber numberWithInt:5]];
NSLog(@"SomeClass number: %d",[[someClass number] intValue]);

The output

2010-04-02 12:42:09.260 SomeClass App[8842:207] SomeClass number: 0

 

[CMT]

Have you initialized the object someClass correctly?

And, imported the class .h where you want to use it?

Using exactly the class you posted here, I created a command line tool with the following main file:

#import <Foundation/Foundation.h>
#import "SomeClass.h"

int main (int argc, const char * argv[]) {
    NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];

    SomeClass *myObject = [[SomeClass alloc] init];
	
	[myObject setNumber:[NSNumber numberWithInt:5]];
	
	NSLog(@"SomeClass number: %d", [[myObject number] intValue]);
	
	// or
	
	NSLog(@"SomeClass number by dot notation: %d", [myObject.number intValue]);
	
	[myObject release];
	
    [pool drain];
    return 0;
}

Which worked perfectly, printing:

2

010-04-03 10:44:48.877 number[1277:a0f] SomeClass number: 5
2010-04-03 10:44:48.880 number[1277:a0f] SomeClass number by dot notation: 5

Hope this helps to identify where is the bug!

 

[seepel]

Have you initialized the object someClass correctly?

And, imported the class .h where you want to use it?

Using exactly the class you posted here, I created a command line tool with the following main file:
...
Hope this helps to identify where is the bug!

I must have had some other messy code somewhere that was interferring. I scrapped everything and started over and you're right, it does work as expected. Thank you.