iPhone alloc and release

Question

i am new in ObjC and iPhone.

I downloaded an example of data sharing between multiple views. The basic approach is to create an data model object in the base UIApplication and get/set data from/to it. So in the init method i saw the following code:

- (id) init;
{
    self.theAppDataObject = [[ExampleAppDataObject alloc] init];
    [theAppDataObject release];
    return [super init];
}

And after that, using delegate we can access this object.

id theDelegate = (id) [UIApplication sharedApplication].delegate;
    ExampleAppDataObject* theDataObject;
    theDataObject = (ExampleAppDataObject*) theDelegate.theAppDataObject;

So, my question is in the first code example. Why do we need to alloc memory for the theAppDataObject object, and immediately after that - release the object? Why don't we get nil when accessing this object later?

10x

Answer 1

I assume theAppDataObject is declared as @property (retain). Therefore, when setting the object by doing self.theAppDataObject (or [self setTheAppDataObject:]), this property will retain the ExampleAppDataObject. Therefore, you can release it afterwards.

When you alloc and init the ExampleAppDataObject, it's retain count goes up to 1. When you set the AppDataObject to this ExampleAppDataObject, it sends retain to it, so the retain count goes up to 2. You can then release your own ownership of the object; it won't get deallocated because theAppDataObject still has ownership.

If that makes sense.