How to set the action for a UIBarButtonItem in Swift

How can the action for a custom UIBarButtonItem in Swift be set?

The following code successfully places the button in the navigation bar:

var b = UIBarButtonItem(title: "Continue", style: .Plain, target: self, action:nil)
self.navigationItem.rightBarButtonItem = b

Now, I would like to call func sayHello() { println("Hello") } when the button is touched. My efforts so far:

var b = UIBarButtonItem(title: "Continue", style: .Plain, target: self, action:sayHello:)
// also with `sayHello` `sayHello()`, and `sayHello():`

and..

var b = UIBarButtonItem(title: "Continue", style: .Plain, target: self, action:@selector(sayHello:))
// also with `sayHello` `sayHello()`, and `sayHello():`

and..

var b = UIBarButtonItem(title: "Continue", style: .Plain, target: self, action:@selector(self.sayHello:))
// also with `self.sayHello` `self.sayHello()`, and `self.sayHello():`

Note that sayHello() appears in the intellisense, but does not work.

Thanks for your help.

EDIT: For posterity, the following works:

var b = UIBarButtonItem(title: "Continue", style: .Plain, target: self, action:"sayHello")

As of Swift 2.2, there is a special syntax for compiler-time checked selectors. It uses the syntax: #selector(methodName).

Swift 3 and later:

var b = UIBarButtonItem(
    title: "Continue",
    style: .plain,
    target: self,
    action: #selector(sayHello(sender:))
)

func sayHello(sender: UIBarButtonItem) {
}

If you are unsure what the method name should look like, there is a special version of the copy command that is very helpful. Put your cursor somewhere in the base method name (e.g. sayHello) and press Shift+Control+Option+C. That puts the ‘Symbol Name’ on your keyboard to be pasted. If you also hold Command it will copy the ‘Qualified Symbol Name’ which will include the type as well.

Swift 2.3:

var b = UIBarButtonItem(
    title: "Continue",
    style: .Plain,
    target: self,
    action: #selector(sayHello(_:))
)

func sayHello(sender: UIBarButtonItem) {
}

This is because the first parameter name is not required in Swift 2.3 when making a method call.

You can learn more about the syntax on swift.org here: https://swift.org/blog/swift-2-2-new-features/#compile-time-checked-selectors

Swift 4/5 example

button.target = self
button.action = #selector(buttonClicked(sender:))

@objc func buttonClicked(sender: UIBarButtonItem) {
        
}

Swift 5 & iOS 13+ Programmatic Example

1. You must mark your function with @objc, see below example!
2. No parenthesis following after the function name! Just use #selector(name).
3. private or public doesn't matter; you can use private.

Code Example

override func viewWillAppear(_ animated: Bool) {
    super.viewWillAppear(animated)
    
    let menuButtonImage = UIImage(systemName: "flame")
    let menuButton = UIBarButtonItem(image: menuButtonImage, style: .plain, target: self, action: #selector(didTapMenuButton))
    navigationItem.rightBarButtonItem = menuButton
}

@objc public func didTapMenuButton() {
    print("Hello World")
}