Programming iOS 6, 3rd Edition

Outlet Connections

You know how to load a nib file, thus instantiating its top-level nib objects. But those instances are useless to you if you don’t know how to get a reference to any of them in your code! Doing things with an object such as a label or a button or a text field or whatever (such as setting or getting the text it displays) is easy; but you have to be able to talk to the object in the first place, meaning that you need a reference to it, a variable that points to that instance (Chapter 3). Getting a reference to an instance that you created in code is trivial, because you assigned it to a variable at the time you created it (Chapter 5). But there’s no such assignment when you load a nib; you just load it and that’s the end of that:

[[NSBundle mainBundle] loadNibNamed:@"MyNib" owner:mc options:nil];
// no assignment??!! dude, where are my nib-created instances?

To refer in code to instances generated from nib objects when the nib loads, you need to have previously set up an outlet connection from a proxy object in the same nib.

A connection is a named unidirectional linkage from one object in a nib file (the connection’s source) to another object in the same nib file (the connection’s target). An outlet is a connection whose name corresponds to an instance variable in the source object. When the nib loads, and the target object is instantiated, the nib-loading mechanism assigns the value of the instance variable to be the target object. Thus the source object winds up ...