Swift:"Unrecognized selector sent to instance", Xcode 9.4.1

Question

Can anyone help me with this?

override func viewDidLoad() {
    super.viewDidLoad()
    tableView.delegate=self
    tableView.dataSource=self
    searchBar.autocorrectionType = .yes
    searchBar.delegate=self
    searchBarView.translatesAutoresizingMaskIntoConstraints=false

    let tap:UIGestureRecognizer = UITapGestureRecognizer(target: self, action: Selector(("tapCancel:")))

    searchBarView.addGestureRecognizer(tap)
    tableView.addGestureRecognizer(tap)
    tableView.isUserInteractionEnabled=true
}
...
func tapCancel(sender:UITapGestureRecognizer){
    hideSearchBarView()
    isSearchon=false
    print("Tap cancel!")
}

Every time I tap the View, it crash. "unrecognized selector sent to instance 0x7feb85d109e0"

I will appreciate any help! Thanks!

Use `#selector(tapCancel)` instead of creating it from a string — dan, Jun 19 '18 at 03:36

Nicolas Miari · Answer 1 · 2018-06-19T05:18:47.933

I believe the reason is due to how method names get mapped between Swift and Objective-C, which underlies the Cocoa implementation and the whole target/action mechanism.

In your case, the Swift method:

@objc func tapCancel(sender:UITapGestureRecognizer)

...corresponds to the Objective-C selector:

-tapCancelWithSender:

Note: In order to work with the target/action paradigm (i.e., called by means of a selector), the method needs to be declared as @objc. The alternative attribute @IBOutlet (for use in conjunction with Interface Builder) also supports this. (tip of the hat to @rmaddy)

In order to remove the "withSender" part and get a selector that matches tapCancel:, you need to tell Swift to remove the argument label sender, like this:

func tapCancel(_ sender:UITapGestureRecognizer) // Notice the underscore (_)

Also, in line with the comment by @dan, perhaps you can use:

#selector(self.tapCancel(_:))

or more succinctly, as pointed by (thanks again) @rmaddy, just:

#selector(tapCancel)

(Xcode will try to autocomplete it to #selector(tapCancel(_:)), but the shorter syntax works as well and the method name is highlighted)

I was not familiar with the Selector() syntax you used, so I tried playing a bit with it, and behold:

(Selector does not match any method the compiler can "see").

(After adding "withSender", the compiler can match the method, but it suggests using the better #selector(... syntax).

As @rmaddy also pointed out in the comments, using the shorter #selector(doSomething) syntax (no colons, no underscore, no self) also does away with the problem of whether "withSender" is needed or not.

You just need `#selector(tapCancel)`. You do not need to add the `_` before the `sender` parameter.. And you need to add `@objc` just before `func tapCancel...` — rmaddy, Jun 19 '18 at 04:59
@rmaddy Thank you, I’ll update the answer as soon as I get to my desk. — Nicolas Miari, Jun 19 '18 at 05:00

score 0 · Answer 2 · answered Jun 19 '18 at 05:42

use

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

instead of

let tap:UIGestureRecognizer = UITapGestureRecognizer(target: self, action: Selector(("tapCancel:")))

And add @objc before method tapCancel()

Swift:"Unrecognized selector sent to instance", Xcode 9.4.1

2 Answers2