Question

If I declare an ivar without property declaration, and this ivar could be used or not during the object life-cycle, do I have to release it in dealloc?

I have sometimes seen that properties are declared as ivar and property, and sometimes only have property declaration. What is the difference? Which is the better way?

Example:

@interface MyClass: NSObject
{
     NSObject *ivar;   // This is sometimes omitted.
}

@property (nonatomic, retain) NSObject *ivar;

@implementation MyClass
@synthesize ivar;

...

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

How come the ivar declaration is sometimes omitted?

The other case is when there is no property declaration:

@interface MyClass: NSObject
{
     NSObject *ivar;
}

@implementation MyClass

-(void)thisMethodCanBeCalledOrNot
{
    ivar = [[NSObject alloc] init];

    [ivar useIt];

   //ivar must be alive for further uses in different methods of this class. For this is not released in this method.
}

...

-(void)dealloc
{
   [ivar release]; //If thisMethodCanBeCalledOrNot is never called, could this cause a over release in ivar?
   [super dealloc];
}

Answer 1

Yes you have to release it. When you call [ivar release], nothing happens if the ivar is nil, but if it contains a pointer to an object, you would cause a memory leak by not releasing it.

It’s preferable to not use self.ivar = nil in the dealloc method, as the setter method could contain logic that is unnecessary during deallocation, or could even cause tricky bugs.

Regarding @property declarations without an explicit ivar declaration, the “modern runtime” synthesizes the ivar automatically.