The init and dealloc idioms.

For C++ programmers the first surprise waiting for them in Objective-C is that in a derived class they must explicitly call the init and dealloc methods of the superclass (roughly the equivalent of a constructor and destructor).

By following the idioms below you can avoid a lot of headaches.

- (id)init
{
    if(self = [super init])
    {
        // how to handle failure
        memberVariable = [[SomeOtherClass alloc] init];
        if(memberVariable == nil)
        {
            [self release];
            return nil;
        }
    }
    return self;
}

- (void)dealloc
{
    // Release anything you alloced or retained...
    [memberVariable release];
    // ... then dealloc your super class
    [super dealloc];
}

When accessing member variables in init and dealloc you show access them directly, not through accessors, to avoid side-effects.

Reference

The Objective-C Programming Language: Allocating and Initializing Objects