[iPhone] Question about properties/ivars and retain/release

Question

I'm not sure I am understanding how the retain/release policy works for properties fully. I have the following property declaration:
@property (nonatomic, retain) AudioPlayer *audioPlayer;
An instance is created using the following code:
self.audioPlayer = [[AudioPlayer alloc] initWithDelegate:self];
If I call the following, the dealloc method of audioPlayer does not get called:
[audioPlayer release];
audioPlayer = nil;
If I call this, the dealloc method does get called:
[audioPlayer release];
self.audioPlayer = nil;
What about setting the pointer to nil using the 'dot' property notation makes the reference count get to zero when it does not in the above code block?

Answer 1

The synthesized property adds 1 to the retain count. But the object was born with a retain count of 1, and 1+1=2.
Splitting the first line into two may make it clearer:
AudioPlayer * temp=[[AudioPlayer alloc] initWithDelegate:self];
allocates the object with a retain count of 1.
self.audioPlayer=temp;
increases the retain count by 1.
To get the result you want (retain count=1), do this:
AudioPlayer * temp=[[AudioPlayer alloc] initWithDelegate:self]; // 1
self.audioPlayer=temp; // 2
[temp release]; // 1
or this:
self.audioPlayer=[[[AudioPlayer alloc] initWithDelegate:self] autorelease];
This creates the object with a retain count of 1, increases the retain count by 1 because the object pointer is being stored into a property, and arranges for the retain count to be decremented by 1 in the not too distant future.
You could also do this:
audioPlayer=[[AudioPlayer alloc] initWithDelegate:self];
which doesn't invoke the property setter but stores the pointer directly in the class variable. If you confine yourself strictly to doing this once only, at the beginning of everything, then it's quite safe. Otherwise the autorelease form is probably the best compromise in terms of readability.