Question

I noticed methods marked optional in several protocols defined in the iPhone SDK, such as the UIActionSheetDelegate protocol for example.

How can I define a protocol of my own, and set a few of the methods as optional?

Answer 1

From the Apple page on ‘Formal Protocols‘:

Optional Protocol methods can be marked as optional using the @optional keyword. Corresponding to the @optional modal keyword, there is a @required keyword to formally denote the semantics of the default behavior. You can use @optional and @required to partition your protocol into sections as you see fit. If you do not specify any keyword, the default is @required.

@protocol MyProtocol  - (void)requiredMethod;  @optional - (void)anOptionalMethod; - (void)anotherOptionalMethod;  @required - (void)anotherRequiredMethod;  @end