IBOutlet in objective-c

Question

what does this line of code do :

IBOutlet UITextField *userName;

Answer 1

IBOutlet exposes variables in Interface Builder.

Example: go to Interface Builder, right click the class containing that line, and you will see a element userName. Unlike the other members of that class, it appears because it has been declared using IBOutlet. If you drag a line from that element to a UITextField control, any operation on the variable (eg: accessing its contents with userName.text) will be performed on the GUI element.