Find method signature for selectors in Objetive-C

Question

Where can I find the method signature for callback methods in built-in classes like UIGestureRecognizer or UIMenuItem etc?

e.g., documentation states for UIMenuItem:

initWithTitle:action:
Creates and returns a menu-item object initialized with the given title and action.

-(id)initWithTitle:(NSString )title action:(SEL)action

Parameters
title
The title of the menu item.
action
A selector identifying the method of the responder object to invoke for handling the command represented by the menu item.
Return Value
An initialized UIMenuItem object, or nil if there was a problem creating the object.

How do I know what parameter 'action' may receive?

Answer 1

Action can be any selector. You can make a selector by using @selector(...) or NSSelectorFromString(...).

Answer 2

'action' is a convention in Cocoa Touch/UIKit : Target-Action in UIKit

Actions can have any of the following three signatures in UIKit:

- (void)action
- (void)action:(id)sender
- (void)action:(id)sender forEvent:(UIEvent *)event

Answer 3

See the documentation for the Target-Action Mechanism in UIKit. Specifically it mentions the following:

In contrast with the Application Kit, where an action method may have only one or perhaps two valid signatures, the UIKit framework allows three different forms of action selector:

• - (void)action
• - (void)action:(id)sender
• - (void)action:(id)sender forEvent:(UIEvent *)event