Swift programmatically create function for button with a closure - swift

Question

In Swift you can create a function for a button like this:
button.addTarget(self, action: #selector(buttonAction), forControlEvents: .TouchUpInside)
However is there a way I can do something like this:
button.whenButtonIsClicked({Insert code here})
That way I do not even have too declare an explicit function for the button. I know I can use button tags but I would prefer to do this instead.

Answer 1

Create your own UIButton subclass to do this:
class MyButton: UIButton {
var action: (() -> Void)?
func whenButtonIsClicked(action: #escaping () -> Void) {
self.action = action
self.addTarget(self, action: #selector(MyButton.clicked), for: .touchUpInside)
}
// Button Event Handler:
// I have not marked this as #IBAction because it is not intended to
// be hooked up to Interface Builder
#objc func clicked() {
action?()
}
}
Substitute MyButton for UIButton when you create buttons programmatically and then call whenButtonIsClicked to set up its functionality.
You can also use this with UIButtons in a Storyboard (just change their class to MyButton) and then call whenButtonIsClicked in viewDidLoad.
#IBOutlet weak var theButton: MyButton!
var count = 0
override func viewDidLoad() {
super.viewDidLoad()
// be sure to declare [unowned self] if you access
// properties or methods of the class so that you
// don't create a strong reference cycle
theButton.whenButtonIsClicked { [unowned self] in
self.count += 1
print("count = \(self.count)")
}
A much more capable implementation
Recognizing the fact that programmers might want to handle more events than just .touchUpInside, I wrote this more capable version which supports multiple closures per UIButton and multiple closures per event type.
class ClosureButton: UIButton {
private var actions = [UInt : [((UIControl.Event) -> Void)]]()
private let funcDict: [UInt : Selector] = [
UIControl.Event.touchCancel.rawValue: #selector(eventTouchCancel),
UIControl.Event.touchDown.rawValue: #selector(eventTouchDown),
UIControl.Event.touchDownRepeat.rawValue: #selector(eventTouchDownRepeat),
UIControl.Event.touchUpInside.rawValue: #selector(eventTouchUpInside),
UIControl.Event.touchUpOutside.rawValue: #selector(eventTouchUpOutside),
UIControl.Event.touchDragEnter.rawValue: #selector(eventTouchDragEnter),
UIControl.Event.touchDragExit.rawValue: #selector(eventTouchDragExit),
UIControl.Event.touchDragInside.rawValue: #selector(eventTouchDragInside),
UIControl.Event.touchDragOutside.rawValue: #selector(eventTouchDragOutside)
]
func handle(events: [UIControl.Event], action: #escaping (UIControl.Event) -> Void) {
for event in events {
if var closures = actions[event.rawValue] {
closures.append(action)
actions[event.rawValue] = closures
} else {
guard let sel = funcDict[event.rawValue] else { continue }
self.addTarget(self, action: sel, for: event)
actions[event.rawValue] = [action]
}
}
}
private func callActions(for event: UIControl.Event) {
guard let actions = actions[event.rawValue] else { return }
for action in actions {
action(event)
}
}
#objc private func eventTouchCancel() { callActions(for: .touchCancel) }
#objc private func eventTouchDown() { callActions(for: .touchDown) }
#objc private func eventTouchDownRepeat() { callActions(for: .touchDownRepeat) }
#objc private func eventTouchUpInside() { callActions(for: .touchUpInside) }
#objc private func eventTouchUpOutside() { callActions(for: .touchUpOutside) }
#objc private func eventTouchDragEnter() { callActions(for: .touchDragEnter) }
#objc private func eventTouchDragExit() { callActions(for: .touchDragExit) }
#objc private func eventTouchDragInside() { callActions(for: .touchDragInside) }
#objc private func eventTouchDragOutside() { callActions(for: .touchDragOutside) }
}
Demo
class ViewController: UIViewController {
var count = 0
override func viewDidLoad() {
super.viewDidLoad()
let button = ClosureButton(frame: CGRect(x: 50, y: 100, width: 60, height: 40))
button.setTitle("press me", for: .normal)
button.setTitleColor(.blue, for: .normal)
// Demonstration of handling a single UIControl.Event type.
// If your closure accesses self, be sure to declare [unowned self]
// to prevent a strong reference cycle
button.handle(events: [.touchUpInside]) { [unowned self] _ in
self.count += 1
print("count = \(self.count)")
}
// Define a second handler for touchUpInside:
button.handle(events: [.touchUpInside]) { _ in
print("I'll be called on touchUpInside too")
}
let manyEvents: [UIControl.Event] = [.touchCancel, .touchUpInside, .touchDown, .touchDownRepeat, .touchUpOutside, .touchDragEnter,
.touchDragExit, .touchDragInside, .touchDragOutside]
// Demonstration of handling multiple events
button.handle(events: manyEvents) { event in
switch event {
case .touchCancel:
print("touchCancel")
case .touchDown:
print("touchDown")
case .touchDownRepeat:
print("touchDownRepeat")
case .touchUpInside:
print("touchUpInside")
case .touchUpOutside:
print("touchUpOutside")
case .touchDragEnter:
print("touchDragEnter")
case .touchDragExit:
print("touchDragExit")
case .touchDragInside:
print("touchDragInside")
case .touchDragOutside:
print("touchDragOutside")
default:
break
}
}
self.view.addSubview(button)
}
}

Answer 2

If you don't want to do anything "questionable" (i.e., using Objective-C's dynamic capabilities, or adding your own touch handlers, etc.) and do this purely in Swift, unfortunately this is not possible.
Any time you see #selector in Swift, the compiler is calling objc_MsgSend under the hood. Swift doesn't support Objective-C's dynamicism. For better or for worse, this means that in order to swap out the usage of this selector with a block, you'd probably need to perform some black magic to make it work, and you'd have to use Objective-C constructs to do that.
If you don't have any qualms about doing "yucky dynamic Objective-C stuff", you could probably implement this by defining an extension on UIButton, and then associate a function to the object dynamically using associated objects. I'm going to stop here, but if you want to read more, NSHipster has a great overview on associated objects and how to use them.

Answer 3

This one will work !
Make sure you don't alter the tag for buttons
extension UIButton {
private func actionHandleBlock(action:(()->())? = nil) {
struct __ {
var closure : (() -> Void)?
typealias EmptyCallback = ()->()
static var action : [EmptyCallback] = []
}
if action != nil {
// __.action![(__.action?.count)!] = action!
self.tag = (__.action.count)
__.action.append(action!)
} else {
let exe = __.action[self.tag]
exe()
}
}
#objc private func triggerActionHandleBlock() {
self.actionHandleBlock()
}
func addAction(forControlEvents control :UIControlEvents, ForAction action:#escaping () -> Void) {
self.actionHandleBlock(action: action)
self.addTarget(self, action: #selector(triggerActionHandleBlock), for: control)
}
}

Answer 4

You can also just subclass UIView and have a property that is a closure like vacawama has.
var action: () -> ()?
Then override the touchesBegan method to call the function whenever the button is touched. With this approach though you don't get all the benefits of starting with a UIBitton.

Answer 5

let bt1 = UIButton(type: UIButtonType.InfoDark)
bt1.frame = CGRectMake(130, 80, 40, 40)
let bt2 = UIButton(type: UIButtonType.RoundedRect)
bt2.frame = CGRectMake(80, 180, 150, 44)
bt2.backgroundColor = UIColor.purpleColor()
bt2.tintColor = UIColor.yellowColor()
bt2.setTitle("Tap Me", forState: UIControlState.Normal)
bt2.addTarget(self, action: "buttonTap", forControlEvents: UIControlEvents.TouchUpInside)
let bt3 = UIButton(type: UIButtonType.RoundedRect)
bt3.backgroundColor = UIColor.brownColor()
bt3.tintColor = UIColor.redColor()
bt3.setTitle("Tap Me", forState: UIControlState.Normal)
bt3.frame = CGRectMake(80, 280, 150, 44)
bt3.layer.masksToBounds = true
bt3.layer.cornerRadius = 10
bt3.layer.borderColor = UIColor.lightGrayColor().CGColor
self.view.addSubview(bt1)
self.view.addSubview(bt2)
self.view.addSubview(bt3)
}
func buttonTap(button:UIButton)
{
let alert = UIAlertController(title: "Information", message: "UIButton Event", preferredStyle: UIAlertControllerStyle.Alert)
let OKAction = UIAlertAction(title: "OK", style: UIAlertActionStyle.Default, handler: nil)
alert.addAction(OKAction)
}