Protocol versus Category

Question

Can anyone explain the differences between Protocols and Categories in Objective-C? When do you use one over the other?

Answer 1

A protocol allows you to declare a list of methods which are not confined to any particular class or categories. The methods declared in the protocol can be adopted any class/categories. A class or category which adopts a protocol must implements all the required methods declared in the protocol.

A category allows you to add additional methods to an existing class but they do not allow additional instance variables. The methods the category adds become part of the class type.