How to add action to any view object using Tap Gesture

Akash Gupta

28 January 2019

What is Tap Gesture:

If you’ve ever used an iOS device, then, whether you know it or not, you’ve used tap gesture recognition on many occasions. like double tapping functionality, add action to non-clickable view objects etc. All of these actions are done by tap gesture recognizers.

Disadvantage:

The worst part about adding a UITapGestureRecognizer or any sort of gesture recognizer/target action is implementing a new function solely for the selector parameter. For this, I’d like to share a neat trick I threw together that lets you add gesture recognizers without selectors.

Implementation:

Let’s say we have anUIImageView in our View Controller and we want to add a UITapGestureRecognizer to it that prints out a statement whenever it’s tapped.

Normally we would create an instance of a UITapGestureRecognizer and set a target to the View Controller and its selector as some function we quickly threw together (myImageViewTapped(sender: UITapGestureRecognizer)). This can get a bit redundant and can lead to messy code with functions for every subview you want to add interactivity too.

I got to thinking that I could just make a quick extension that adds tap gesture recognizers to my image view for me, but then I’d have to make a new function for each recognizer, right? Wrong! Using the power of associated objects, we can actually store closures as computed properties in our extension!

extension UIView {

    fileprivate struct AssociatedObjectKeys {
        static var tapGestureRecognizer = "MyAssociatedObjectKeyForTapGesture"
    }

    fileprivate typealias Action = (() -> Void)?

    fileprivate var tapGestureRecognizerAction: Action? {
        set {
            if let newValue = newValue {
                objc_setAssociatedObject(self, &AssociatedObjectKeys.tapGestureRecognizer, newValue, objc_AssociationPolicy.OBJC_ASSOCIATION_RETAIN)
            }
        }
        get {
            let tapGestureRecognizerActionInstance = objc_getAssociatedObject(self, &AssociatedObjectKeys.tapGestureRecognizer) as? Action
            return tapGestureRecognizerActionInstance
        }
    }

    public func addTapGestureRecognizer(action: (() -> Void)?) {
        self.isUserInteractionEnabled = true
        self.tapGestureRecognizerAction = action
        let tapGestureRecognizer = UITapGestureRecognizer(target: self, action: #selector(handleTapGesture))
        self.addGestureRecognizer(tapGestureRecognizer)
    }

    @objc fileprivate func handleTapGesture(sender: UITapGestureRecognizer) {
        if let action = self.tapGestureRecognizerAction {
            action?()
        } else {
            print("no action")
        }
    }
}

extension UIView {

fileprivate struct AssociatedObjectKeys {

static var tapGestureRecognizer = "MyAssociatedObjectKeyForTapGesture"

}

fileprivate typealias Action = (() -> Void)?

fileprivate var tapGestureRecognizerAction: Action? {

set {

if let newValue = newValue {

objc_setAssociatedObject(self, &AssociatedObjectKeys.tapGestureRecognizer, newValue, objc_AssociationPolicy.OBJC_ASSOCIATION_RETAIN)

}

get {

let tapGestureRecognizerActionInstance = objc_getAssociatedObject(self, &AssociatedObjectKeys.tapGestureRecognizer) as? Action

return tapGestureRecognizerActionInstance

}

public func addTapGestureRecognizer(action: (() -> Void)?) {

self.isUserInteractionEnabled = true

self.tapGestureRecognizerAction = action

let tapGestureRecognizer = UITapGestureRecognizer(target: self, action: #selector(handleTapGesture))

self.addGestureRecognizer(tapGestureRecognizer)

}

@objc fileprivate func handleTapGesture(sender: UITapGestureRecognizer) {

if let action = self.tapGestureRecognizerAction {

action?()

} else {

print("no action")

}

Uses:

override func viewDidLoad() {
    super.viewDidLoad()
    
    myImageView.addTapGestureRecognizer {
        print("Image tapped")
    }
}

override func viewDidLoad() {

super.viewDidLoad()

myImageView.addTapGestureRecognizer {

print("Image tapped")

}

Thank You!!!