Why @objc in "UITapGestureRecognizer"?

Question

I added UITapGestureRecognizer to my UIView. But I don't understand why I have to use @objc to use UITapGestureRecognizer.

In particular, the difference between Selector? and #selector is too confusing.

And I didn't see an explanation using @objc in the official document of the Apple developer.

import UIKit

class ViewController: UIViewController {
    override func viewDidLoad() {
        super.viewDidLoad()

        let viw = UIView(frame: CGRect(x: 0, y: 0, width: 200, height: 200))
        viw.center = self.view.center
        viw.backgroundColor = UIColor.black
        self.view.addSubview(viw)

        let tap = UITapGestureRecognizer(target: self, action: #selector(handleTap(sender:)))
        viw.addGestureRecognizer(tap)
    }

    @objc func handleTap(sender: UITapGestureRecognizer) {
        if sender.state == .ended {
            print(1)
        }
    }
}

I think this is an old way. If there is an up-to-date way to add UITapGestureRecognizer to UIView, I would like to know that.

Answer 1

Why @objc ?

If you are using any class selectors which is basically written in Objective-C than you need to add @objc before that function so that UITapGestureRecognizer class can revert back with proper event.

If you are not adding @objc before your gesture handler function compiler will throw error as mention below :

Argument of '#selector' refers to instance method 'handleTap()' that is not exposed to Objective-C

It clearly says that you haven't exposed your handle for Objective-C.

Apple Officially link for Language Interoperability

https://developer.apple.com/documentation/swift#2984801

Also check this link for more info on

Use runtime Obj C features in Swift

Hope you can get your answer form above explanation!