Question

Given the piece of code below where blueViewController is an iVar.
Question: Why not instantiate the iVar directly?

BlueViewController *blueController = [[BlueViewController alloc]initWithNibName:@"BlueView" bundle:nil];
self.blueViewController = blueController;
[blueController release];

Answer 1

It depends on where you are in your class. If you are in your init (and dealloc) method it is recommended to refer to the ivar directly to avoid any side effects in setter logic. Therefore in the init I would do

_blueViewController = [[BlueViewController alloc] initWithNibName:@"BlueView" bundle:nil];

But anywhere else I would do it how you have done it. Then if there is any custom logic in the getter/setter I know it will be run.

To eleborate on @Vladimar’s point the synthesized setter for a retain will do some memory management similar to this:

- (void)setMyObject:(MyObject *)newMyObject
{
  // If it's the same object we don't need to do anything
  if (_myObject != newMyObject) {
    [newMyObject retain];
    [_myObject release];
    _myObject = newMyObject;
  }
}

It is much safer to let the getters/setters worry about all this logic any time you set your ivars.