Swift 2 unrecognized selector in tapgesture

Question

I recently started to update my app to Swift 2.0, but I've run into a problem that has a hundred different answers on SO, none of which seemed to be related to my problem.

(This worked before updating the application to Swift 2.0), but I havn't been able to find any changes made to tap gesture recognisers?

Here's the full error I'm getting:

[Stocks.SidePanelViewController proFormulaTapGesture]: unrecognized selector sent to instance 0x14f06ae00

Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[Stocks.SidePanelViewController proFormulaTapGesture]: unrecognized selector sent to instance 0x14f06ae00'

*** First throw call stack: (0x1830904d0 0x197afff9c 0x1830971ec 0x183094188 0x182f9920c 0x188c3c58c 0x188899b50 0x18872d104 0x188c3bc30 0x1886ed28c 0x1886eb3ac 0x18872b088 0x18872a5ec 0x1886fb908 0x1886f9fac 0x183047d6c 0x183047800 0x183045500 0x182f75280 0x18e0ec0cc 0x188762df8 0x100158184 0x1983428b8) libc++abi.dylib: terminating with uncaught exception of type NSException

It's a simple tap gesture. But it seems to not recognize the selector anymore.

Here's the code I use to set up the recognizer:

let proFormulaTap = UITapGestureRecognizer()

proFormulaTap.addTarget(self, action:"proFormulaTapGesture")
proFormulaView.addGestureRecognizer(proFormulaTap)

Here's the function I'm trying to run:

func proFormulaTapGesture() throws {
        print("proFormulaTapGesture")
        selectView(proFormulaView)
        selectedMenuItem = 0
        Formula = 1
        menuTabBarController.selectedIndex = 0
        navigationController?.navigationBar.topItem!.title = "BASIC FORMULA"
        try (menuTabBarController.viewControllers as! [SuggestionsViewController])[0].loadSuggestions()
    }

However since it never prints "proFormulaTapGesture" in the console. I definitely think the error occurs before the function. Also suggested by the error mentioning the selector.

Obviously try/catch has been added to the function since the update to Swift 2.0, but nothing has been changed in the setup of the tapGestureRecognizer.

I tried removing the "throws" and try from the function, but the problem perists. I also tried making a button instead of a tap gesture recognizer. But I'm still getting the same error, suggesting it might be a problem with the selector (function) and not the tap gesture / button. However all my other buttons in my app works just fine?

I also tried to rename the selector/function, and the tap gesture recognizer. Still the same.

The original Code was programmed in Swift, not Obj-C. The throws and try, was added during Apple's code conversion to Swift 2.0

Any help to why this is suddenly broken would be greatly appreciated.

Thanks!

Answer 1

The issue may be that UIKit does not know how to call a selector that throws, at least in this context.

Remember that UIKit will be calling this function in response to a tap action. It is not accustomed to calling a function that throws; obviously the throw must alter the method's call signature as far as the Objective-C runtime is concerned. Beyond that, if your function proFormulaTapGesture did throw an error, what would UIKit do with the error even if it could catch it?

I'm not sure where you added do/try/catch. But unless it was inside your action function proFormulaTapGesture, I do not see how it could be relevant. I believe that you will need to implement the try/catch error handling inside proFormulaTapGesture, so that it effectively swallows the error, so that proFormulaTapGesture does not throw.

I just created a quick test project myself and found that a throwing target action gives the same "Unrecognized selector" error you got:

override func viewDidLoad() {
    super.viewDidLoad()

    self.tapper = NSClickGestureRecognizer(target: self, action: "didClick")
    self.view.addGestureRecognizer(self.tapper!)
}

func didClick() throws {
    print("did click")
}

2015-07-27 00:16:43.260 Test1[71047:54227175] -[Test1.ViewController didClick]: unrecognized selector sent to instance 0x6000000c5010

...

I believe you will need to rework your code to handle the error internally in your action function so that it does not throw - something like this:

func proFormulaTapGesture() {
    print("proFormulaTapGesture")
    selectView(proFormulaView)
    selectedMenuItem = 0
    Formula = 1
    menuTabBarController.selectedIndex = 0
    navigationController?.navigationBar.topItem!.title = "BASIC FORMULA"
    do {
        try (menuTabBarController.viewControllers as! [SuggestionsViewController])[0].loadSuggestions()
    } catch {
        // Handle the error here somehow
    }
}

If you are unable to handle the error within proFormulaTapGesture, you'll have to be more creative with passing it out of the function (think NSNotification, etc...).

---

To be clear, I created a new Single View iOS application in Xcode 7 beta 4, and used this exact code as my ViewController. No other changes. The app compiles and works just fine in the iOS simulator.

@robertvojta also points out that if didTap below is marked private, @objc is also required to avoid a dynamic dispatch crash.

import UIKit

class ViewController: UIViewController {

    var tapper: UITapGestureRecognizer?

    override func viewDidLoad() {
        super.viewDidLoad()

        self.tapper = UITapGestureRecognizer(target: self, action: "didTap")
        self.view.addGestureRecognizer(self.tapper!)
    }

    func didTap() {
        print("did Tap")
    }

}

(Note I also tested on an OS X project, which is the code I used earlier in the answer).