Obj-c: Custom Object handling

Question

I am creating my own custom object, and I am wondering if I need to retain my properties or use something else such as copy (which does what?)?

@interface Asset : NSObject {
    NSString *name;
    NSNumber *assetId;
    NSNumber *linkId;
    NSNumber *parentId;
}

@property (nonatomic, retain) NSString *name; // should I use retain here or something else?
@property (nonatomic, retain) NSNumber *assetId;
@property (nonatomic, retain) NSNumber *linkId;
@property (nonatomic, retain) NSNumber *parentId;

@end

Also, in my .m, do I also need synthesize as well as release?

Daniel Dickison · Accepted Answer · 2011-01-11 20:53:05Z

4

The chapter on Declared Properties in The Objective-C Programming Language explains what copy does and about synthesizing accessors.

answered Jan 11, 2011 at 20:53

Daniel Dickison

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Comments

Gareth Davis · Accepted Answer · 2011-01-11 21:14:13Z

1

My personal preference:

@interface Asset : NSObject {
    // no need to declare them here the @synthesize in the .m will sort all that out
}


// use copy for NSString as it is free for NSString instances and protects against NSMutableString instances being passed in...thanks to @bbum for this
@property (nonatomic, copy) NSString *name;

// no need for copy as NSNumber is immutable
@property (nonatomic,retain) NSNumber *assetId;
@property (nonatomic,retain) NSNumber linkId;
@property (nonatomic,retain) NSNumber parentId;

@end

edited Jan 11, 2011 at 21:14

answered Jan 11, 2011 at 20:59

Gareth Davis

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3 Comments

bbum Over a year ago

You should use copy; it is free for NSString and defense against someone passing in a mutable string.

Gareth Davis Over a year ago

ah.. well that's something I've learnt today...is it also free on NSNumbers?

Daniel Dickison Over a year ago

probably; copy is generally free on non-mutable objects (including things like NSArray).

seand · Accepted Answer · 2011-01-11 21:01:38Z

1

For typical cases your .m will have lines like this:

@synthesize name;
...

That tells the compiler to automatically emit the getter/setter methods. You can also write/override these yourself. So, when someone does a fooAsset.name = x, your object will retain its own reference to 'x'. The other thing you need is a dealloc method to release the references to your members:

- (void)dealloc {
    [name release];
    ....
    [super dealloc];
}

Note that it'll still be appropriate if 'name' is never assigned; nil will silently eat the 'release' message.

answered Jan 11, 2011 at 21:01

seand

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