Objective-C: Do you have to dealloc property objects before deallocating the parent object?

Question

Let's say I have an object named "foo" with another object named "bar" as property.

When "foo" deallocates, will it automatically remove all references to "bar" so that "bar" deallocates as well? or will "foo" deallocate and "bar" float in memory somewhere? even if all of "bar"'s references are defined in "foo".

thanks in advance.

Answer 1

If the foo object has any retains on or copies of (thanks Dave) bar, for example when you declare the property as either one of these:

@property (nonatomic, retain) NSString *bar;
// Or
@property (nonatomic, copy) NSString *bar;

You'll need to release bar when you deallocate foo:

- (void)dealloc
{
    [bar release];

    [super dealloc];
}

The system won't free bar's memory space for you until you get rid of all references to it (i.e. reference count goes down to 0), so you'll have to monitor your reference counts and objects yourself.

Answer 2

If you allocate memory you have to release it. So, yes, put a call to [bar release] or self.bar = nil (if you're using synthesized properties and all that) in your dealloc.

See here for an intro to memory management on iOS.