swift UITapGestureRecognizer not working on view

Question

I had to create a new thread bcoz it's driving me crazy and all the other answers online are exactly the same. I have done this countless of times but I cannot see what I am missing for the life of me. I am using a "test" view controller just to get the tap gesture working but it isn't working at all... I am fairly certain that I am setting this up correctly, as this is how I've always implemented it in the past: (yes, I have checked the box for isUserInteractionEnabled). I am even implementing this on a different viewcontroller this exact way and it is working...

class TestViewController: UIViewController {

  override func viewDidLoad() {
    super.viewDidLoad()
    view.addGestureRecognizer(tap)
  }

  let tap = UITapGestureRecognizer(target: self, action: #selector(wasTapped))

    
  @objc func wasTapped() {
    print("tapped")
  }
}

I have also tried adding the parameters to wasTapped:

@objc func wasTapped(gestureRecognizer: UITapGestureRecognizer) {
  print("tapped")
}

score 14 · Accepted Answer · answered Nov 15 '17 at 01:28

14

You are saying:

override func viewDidLoad() {
    super.viewDidLoad()

    view.addGestureRecognizer(tap)
}

let tap = UITapGestureRecognizer(target: self, action: #selector(wasTapped))

The problem is the last line:

let tap = UITapGestureRecognizer(target: self, action: #selector(wasTapped))

You cannot just say let tap like that in the middle of nowhere. You are implicitly making an instance property. But you cannot initialize an instance property with a target of self, because self does not exist at the time an instance property is initialized. (I regard the fact that that code even compiles as a bug, and have reported it as such.)

Move that line to the start of viewDidLoad, like this:

override func viewDidLoad() {
    super.viewDidLoad()

    let tap = UITapGestureRecognizer(target: self, action: #selector(wasTapped))
    view.addGestureRecognizer(tap)
}

answered Nov 15 '17 at 01:28

matt

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Although the first answer was also correct, I am choosing this one because of the explanation. I wanted to learn why, not just how. This makes total sense and I feel silly for not thinking about that. Thank you. – user7804097 Nov 15 '17 at 05:01
@matt as target takes an Any? is it the case "self" is referring to the viewcontroller type here rather than the instance? – jeh Apr 12 '20 at 16:37
1

@jeh In the "buggy" version where the OP says `let tap` at the top level of the view controller, _yes_, that is exactly what `self` turns out to mean. That's the problem. – matt Apr 12 '20 at 16:48

Mannopson · Answer 2 · 2018-01-25T05:32:49.993

9

Try something like this

override func viewDidLoad() {
    super.viewDidLoad()

     let tap = UITapGestureRecognizer(target: self, action: #selector(wasTapped(sender:)))
     tap.numberOfTapsRequired = 1 // Default value
     view.isUserInteractionEnabled = true
     view.addGestureRecognizer(tap)

}

@objc func wasTapped(sender: UITapGestureRecognizer) {
    print("tapped")
}

edited Jan 25 '18 at 05:32

answered Nov 15 '17 at 01:10

Mannopson

2,634
1
16
32

MQLN · Answer 3 · 2017-11-15T00:47:30.260

5

You have to enable interaction if you want to use gesture recognizers for standard UIView's

Add view.isUserInteractionEnabled = true in your viewDidLoad.

edited Nov 15 '17 at 00:47

answered Nov 15 '17 at 00:42

MQLN

2,292
2
18
33

This issue still occurs when isUserInteractionEnabled is set to true, FWIW. At least it does on iOS 15.4. – Mar 23 '22 at 15:57

score 1 · Answer 4 · edited Aug 04 '20 at 08:09

var tapGesture = UITapGestureRecognizer()

take a view and set IBOutlet like:

@IBOutlet weak var viewTap: UIView!

Write pretty code on viewDidLoad() like:

tapGesture = UITapGestureRecognizer(target: self, action: #selector(self.myviewTapped(_:)))
tapGesture.numberOfTapsRequired = 1
tapGesture.numberOfTouchesRequired = 1
viewTap.addGestureRecognizer(tapGesture)
viewTap.isUserInteractionEnabled = true

this method is calling when tap gesture recognized:

@objc func myviewTapped(_ sender: UITapGestureRecognizer) {
  if self.viewTap.backgroundColor == UIColor.yellow {
    self.viewTap.backgroundColor = UIColor.green
  }else{
    self.viewTap.backgroundColor = UIColor.yellow
  }
}

swift UITapGestureRecognizer not working on view

4 Answers4