CODEWITHSUNDEEP
iosswiftuigesturerecognizer
Opus1217
Opus1217

Reputation: 743

Why doesn't my View respond to a gesture using a gestureRecognizer?

Having just spent a day beating my head against the keyboard, I thought I'd share my diagnosis and solution.

Situation: You add a custom View of custom class CardView to an enclosing view myCards in your app and want each card to respond to a tap gesture (for example to indicate you want to discard the card). Typical code you start with:

In your ViewController:

class MyVC : UIViewController, UIGestureRecognizerDelegate {
...
    func discardedCard(sender: UITapGestureRecognizer) {
        let cv : CardView = sender.view! as! CardView
         ...
    }

In your myCards construction:

cv  = CardView(card: card)
myCards.addSubview(cv)
cv.userInteractionEnabled = true
...
let cvTap = UITapGestureRecognizer(target: self, action: Selector("discardedCard:"))
cvTap.delegate = self
cv.addGestureRecognizer(cvTap)

I found the arguments here very confusing and the documentation not at all helpful. It isn't clear that the target: argument refers to the class that implements discardedCard(sender: UITapGestureRecognizer) . If you're constructing the recognizer and cards in your ViewController that's going to be self. If you want to move the discardedCard into your custom View class (for example), then replace self with CardView in my example, including on the delegate line.

Testing the above code, I found that the discardedCard function was never called. What was going on?

Upvotes: 1

Views: 108

Answers (1)

Opus1217
Opus1217

Reputation: 743

So a day later, here's what I had to fix. I hope this checklist is useful to somebody else. I'm new to iOS (coming from Android), so it may be obvious to you veterans:

  1. Make sure the touched view (cv in the example) has userInteractionEnabled=true . Note that if you use your own constructor it will be set false by default
  2. Make sure all enclosing views also have userInteractionEnabled=true
  3. Others have posted that the order of the delegate statement and addGestureRecognizer statement made a difference; I didn't find that using Xcode 7.2 and iOS 9.2
  4. Most important: Make sure your touched view is fully within the bounds of the enclosing views. In my example, I was building a myCards container that didn't have the width set correctly and was cutting off the right-most cards (and since clipping is disabled by default, this wasn't visually obvious until I looked in the debugger at the View hierarchy)

Upvotes: 1

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