what does @synthesize someProp = _someProp do in a subclass

Question

I'm kind of confused about something. So I understand the memory management portion of doing something like

self.someProp = someObject;

But when you declare something as

@synthesize someProp = _someProp;

and you try to access _someProp in a subclass of the object, I get an error sayint that _someProp has not been declared. But if I do self.someProp I dont' get the error. Can someone explain what the differences are in these scenarios? Thanks.

score 3 · Accepted Answer · answered Feb 23 '12 at 20:10

3

It basically creates the following code:

@implementation myClass
{
    @private
    id _someProp; // notice it's a private implementation property
}

-(id) someProp
{
    return _someProp;
}

-(void) setSomeProp:(id) prop
{
   [_someProp release];
   _someProp = [prop retain];
}

@end

The private implementation property means that it cannot be accessed outside of the class, and isn't a part of the interface, but a part of the implementation.

answered Feb 23 '12 at 20:10

Richard J. Ross III

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If in the interface, you have a declared ivar of _someProp, then this is available to subclasses right since it's now part of the interface? Thx – J W Feb 23 '12 at 21:11
@JW Yes, assuming that you don't declare the iVar as private. – Richard J. Ross III Feb 23 '12 at 22:18

score 1 · Answer 2 · answered Feb 23 '12 at 20:11

1

@synthesize someProp = _someProp; creates getter and setter methods in your class. The methods are named someProp and setSomeProp. These method get and set a private variable named _someProp which is why that name is not available to your subclasses.

answered Feb 23 '12 at 20:11

picciano

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what does @synthesize someProp = _someProp do in a subclass

2 Answers2