iOS ARC, @property, alloc/init

[larswik]

Hey, quick question that I am not 100% sure about. I am using ARC to release my objects automatically. If I have an @property do I still need to alloc/ init an object?

Example

@property (nonatomic, retain) NSMutableDictionary *charDict;
@synthesize charDict;

charDict = [NSMutableDictionary alloc]init];

Since I set up retain in the @properties the object should be retained. So if I alloc/init the dict it feels like I am adding another retain count to it even though ARC handles the release of the object.

 

[Duncan C]

Hey, quick question that I am not 100% sure about. I am using ARC to release my objects automatically. If I have an @property do I still need to alloc/ init an object?

Example

@property (nonatomic, retain) NSMutableDictionary *charDict;
@synthesize charDict;

charDict = [NSMutableDictionary alloc]init];

Since I set up retain in the @properties the object should be retained. So if I alloc/init the dict it feels like I am adding another retain count to it even though ARC handles the release of the object.

A property is just a pointer that can contain an object. Until you allocate an object and store it there, the property is nil.

So yes, you must still alloc/init in ARC.

ARC takes care of object ownership for you. Before ARC, you had to worry about whether a method call gave you an owning reference (retained) to an object, or a non-owning (autoreleased) reference. For owning references, you had to make sure you sent the object a release/autorelease when you were done with it.

With ARC, the system takes care of tracking object ownership for you. As soon as the last owning reference to an object goes out of scope, or is set to nil, the object is released.

 

[CodeBreaker]

Hey, quick question that I am not 100% sure about. I am using ARC to release my objects automatically. If I have an @property do I still need to alloc/ init an object?

Example

@property (nonatomic, retain) NSMutableDictionary *charDict;
@synthesize charDict;

charDict = [NSMutableDictionary alloc]init];

Since I set up retain in the @properties the object should be retained. So if I alloc/init the dict it feels like I am adding another retain count to it even though ARC handles the release of the object.

Also, use strong and weak in place of retain and assign for ARC.

 

[larswik]

A property is just a pointer that can contain an object. Until you allocate an object and store it there, the property is nil.

And by containing an object this means that I do not also need to declare my iVar?

Just sudo code,

@interface WelcomeVC :NSObject{

    [COLOR="Red"]SomeClass *object;[/COLOR]
}
@property(strong) SomeClass *object;

@implementation WelcomeVC
@synthesize object:

-(void)xyz{
   object = [[SomeClass alloc]init];
}

-

Am I able to just declare my iVars at the property line of code instead of between the brackets in the header, {my iVars}? The code above is redundant with the same iVar declared twice, right?

 

[Duncan C]

And by containing an object this means that I do not also need to declare my iVar?

Just sudo code,

@interface WelcomeVC :NSObject{

    [COLOR="Red"]SomeClass *object;[/COLOR]
}
@property(strong) SomeClass *object;

@implementation WelcomeVC
@synthesize object:

-(void)xyz{
   object = [[SomeClass alloc]init];
}

-

Am I able to just declare my iVars at the property line of code instead of between the brackets in the header, {my iVars}? The code above is redundant with the same iVar declared twice, right?

Right.

That's a fairly recent change. Apple extended Objective C so that properties now auatomatically define an iVar to go with each property. By default, the iVar that backs a property has the same name as the property but a "_" prefix.

You also no longer need the @synthesize statement.

 

[larswik]

Thanks.