Protocols

For every object that can have a delegate, there is a corresponding protocol that declares the messages that the object can send its delegate. The delegate implements methods from the protocol for events it is interested in. When a class implements methods from a protocol, it is said to conform to the protocol.

(If you are coming from Java or C#, you would use the word interface instead of protocol.)

The protocol for UITextField’s delegate looks like this:

@​p​r​o​t​o​c​o​l​ ​U​I​T​e​x​t​F​i​e​l​d​D​e​l​e​g​a​t​e​ ​<​N​S​O​b​j​e​c​t​>​ @​o​p​t​i​o​n​a​l​ -​ ​(​B​O​O​L​)​t​e​x​t​F​i​e​l​d​S​h​o​u​l​d​B​e​g​i​n​E​d​i​t​i​n​g​:​(​U​I​T​e​x​t​F​i​e​l​d​ ​*​)​t​e​x​t​F​i​e​l​d​;​ -​ ​(​v​o​i​d​)​t​e​x​t​F​i​e​l​d​D​i​d​B​e​g​i​n​E​d​i​t​i​n​g​:​(​U​I​T​e​x​t​F​i​e​l​d​ ...

Get iOS Programming: The Big Nerd Ranch Guide now with O’Reilly online learning.

O’Reilly members experience live online training, plus books, videos, and digital content from 200+ publishers.