Question

i’m new to obj-c and i was just wondering if someone could explain this. Here we add a UIGestureRecognizer to the current view, and then we release it right away, why? If we release it will this not make it useless in the program?

recognizer = [[UIPanGestureRecognizer alloc] initWithTarget:self action:@selector(handlePan:)];

((UIPanGestureRecognizer *)recognizer).minimumNumberOfTouches = 3;

[self.view addGestureRecognizer:recognizer];

[recognizer release];

Answer 1

When you execute:

[self.view addGestureRecognizer:recognizer];

the gesture recognizer retain count is increased. So, the following release just counter-balances the alloc/init action, which returns an object with retain count of 1.

In other words, you can think in these terms:

1. alloc -> retains the object;
2. addGestureRecognizer -> retains the object;

since you want that self.view be the only owner of the gesture recognizer, you call release once to get things back in order. When self.view is deallocated, it will call release on its gesture recognizer and this will be deallocated as well.

If you did not do like that, you would have a memory leak, since when self.view is deallocated, release would be called on the gesture recognizer but this would not be enough to make the retain count drop to zero (because of the initial retain implied by alloc).

Hope this clarifies things a bit.