Adding a closure as target to a UIButton

I have a generic control class which needs to set the completion of the button depending on the view controller.Due to that setLeftButtonActionWithClosure function needs to take as parameter a closure which should be set as action to an unbutton.How would it be possible in Swift since we need to pass the function name as String to action: parameter.

func setLeftButtonActionWithClosure(completion: () -> Void)
{
    self.leftButton.addTarget(<#target: AnyObject?#>, action: <#Selector#>, forControlEvents: <#UIControlEvents#>)
}

Solution 1:

With iOS 14 Apple has finally added this feature to UIKit. However, someone might still want to use this extension because Apple's method signature is suboptimal.

iOS 14:

extension UIControl {
    func addAction(for controlEvents: UIControl.Event = .touchUpInside, _ closure: @escaping()->()) {
        addAction(UIAction { (action: UIAction) in closure() }, for: controlEvents)
    }
}

pre-iOS 14:

extension UIControl {
    func addAction(for controlEvents: UIControl.Event = .touchUpInside, _ closure: @escaping()->()) {
        @objc class ClosureSleeve: NSObject {
            let closure:()->()
            init(_ closure: @escaping()->()) { self.closure = closure }
            @objc func invoke() { closure() }
        }
        let sleeve = ClosureSleeve(closure)
        addTarget(sleeve, action: #selector(ClosureSleeve.invoke), for: controlEvents)
        objc_setAssociatedObject(self, "\(UUID())", sleeve, objc_AssociationPolicy.OBJC_ASSOCIATION_RETAIN)
    }
}

Usage:

button.addAction {
    print("Hello, Closure!")
}

or:

button.addAction(for: .touchUpInside) {
    print("Hello, Closure!")
}

or if avoiding retain loops:

self.button.addAction(for: .touchUpInside) { [unowned self] in
    self.doStuff()
}

(Extension is included here: https://github.com/aepryus/Acheron)

Also note, in theory .primaryActionTriggered could replace .touchUpInside, but it seems to be currently bugged in catalyst, so I'll leave it as is for now.

Solution 2:

Do Not Use This Answer, See Note Below

NOTE: like @EthanHuang said "This solution doesn't work if you have more than two instances. All actions will be overwrite by the last assignment." Keep in mind this when you develop, i will post another solution soon.

If you want to add a closure as target to a UIButton, you must add a function to UIButton class by using extension

Swift 5

import UIKit    
extension UIButton {
    private func actionHandler(action:(() -> Void)? = nil) {
        struct __ { static var action :(() -> Void)? }
        if action != nil { __.action = action }
        else { __.action?() }
    }   
    @objc private func triggerActionHandler() {
        self.actionHandler()
    }   
    func actionHandler(controlEvents control :UIControl.Event, ForAction action:@escaping () -> Void) {
        self.actionHandler(action: action)
        self.addTarget(self, action: #selector(triggerActionHandler), for: control)
    }
}

Older

import UIKit

extension UIButton {
    private func actionHandleBlock(action:(() -> Void)? = nil) {
        struct __ {
            static var action :(() -> Void)?
        }
        if action != nil {
            __.action = action
        } else {
            __.action?()
        }
    }
    
    @objc private func triggerActionHandleBlock() {
        self.actionHandleBlock()
    }
    
    func actionHandle(controlEvents control :UIControlEvents, ForAction action:() -> Void) {
        self.actionHandleBlock(action)
        self.addTarget(self, action: "triggerActionHandleBlock", forControlEvents: control)
    }
}

and the call:

 let button = UIButton()
 button.actionHandle(controlEvents: .touchUpInside, 
 ForAction:{() -> Void in
     print("Touch")
 })