@selector() in Swift?


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I'm trying to create an NSTimer in Swift but I'm having some trouble.

NSTimer(timeInterval: 1, target: self, selector: test(), userInfo: nil, repeats: true)

test() is a function in the same class.


I get an error in the editor:

Could not find an overload for 'init' that accepts the supplied arguments

When I change selector: test() to selector: nil the error disappears.

I've tried:

  • selector: test()
  • selector: test
  • selector: Selector(test())

But nothing works and I can't find a solution in the references.



All Answers
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    Swift itself doesn't use selectors — several design patterns that in Objective-C make use of selectors work differently in Swift. (For example, use optional chaining on protocol types or is/as tests instead of respondsToSelector:, and use closures wherever you can instead of performSelector: for better type/memory safety.)

    But there are still a number of important ObjC-based APIs that use selectors, including timers and the target/action pattern. Swift provides the Selector type for working with these. (Swift automatically uses this in place of ObjC's SEL type.)

    In Swift 2.2 (Xcode 7.3) and later (including Swift 3 / Xcode 8 and Swift 4 / Xcode 9):

    You can construct a Selector from a Swift function type using the #selector expression.

    let timer = Timer(timeInterval: 1, target: object,
                      selector: #selector(MyClass.test),
                      userInfo: nil, repeats: false)
    button.addTarget(object, action: #selector(MyClass.buttonTapped),
                     for: .touchUpInside)
    view.perform(#selector(UIView.insertSubview(_:aboveSubview:)),
                 with: button, with: otherButton)
    

    The great thing about this approach? A function reference is checked by the Swift compiler, so you can use the #selector expression only with class/method pairs that actually exist and are eligible for use as selectors (see "Selector availability" below). You're also free to make your function reference only as specific as you need, as per the Swift 2.2+ rules for function-type naming.

    (This is actually an improvement over ObjC's @selector() directive, because the compiler's -Wundeclared-selector check verifies only that the named selector exists. The Swift function reference you pass to #selector checks existence, membership in a class, and type signature.)

    There are a couple of extra caveats for the function references you pass to the #selector expression:

    • Multiple functions with the same base name can be differentiated by their parameter labels using the aforementioned syntax for function references (e.g. insertSubview(_:at:) vs insertSubview(_:aboveSubview:)). But if a function has no parameters, the only way to disambiguate it is to use an as cast with the function's type signature (e.g. foo as () -> () vs foo(_:)).
    • There's a special syntax for property getter/setter pairs in Swift 3.0+. For example, given a var foo: Int, you can use #selector(getter: MyClass.foo) or #selector(setter: MyClass.foo).

    General notes:

    Cases where #selector doesn't work, and naming: Sometimes you don't have a function reference to make a selector with (for example, with methods dynamically registered in the ObjC runtime). In that case, you can construct a Selector from a string: e.g. Selector("dynamicMethod:") — though you lose the compiler's validity checking. When you do that, you need to follow ObjC naming rules, including colons (:) for each parameter.

    Selector availability: The method referenced by the selector must be exposed to the ObjC runtime. In Swift 4, every method exposed to ObjC must have its declaration prefaced with the @objc attribute. (In previous versions you got that attribute for free in some cases, but now you have to explicitly declare it.)

    Remember that private symbols aren't exposed to the runtime, too — your method needs to have at least internal visibility.

    Key paths: These are related to but not quite the same as selectors. There's a special syntax for these in Swift 3, too: e.g. chris.valueForKeyPath(#keyPath(Person.friends.firstName)). See SE-0062 for details. And even more KeyPath stuff in Swift 4, so make sure you're using the right KeyPath-based API instead of selectors if appropriate.

    You can read more about selectors under Interacting with Objective-C APIs in Using Swift with Cocoa and Objective-C.

    Note: Before Swift 2.2, Selector conformed to StringLiteralConvertible, so you might find old code where bare strings are passed to APIs that take selectors. You'll want to run "Convert to Current Swift Syntax" in Xcode to get those using #selector.


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    Here's a quick example on how to use the Selector class on Swift:

    override func viewDidLoad() {
        super.viewDidLoad()
    
        var rightButton = UIBarButtonItem(title: "Title", style: UIBarButtonItemStyle.Plain, target: self, action: Selector("method"))
        self.navigationItem.rightBarButtonItem = rightButton
    }
    
    func method() {
        // Something cool here   
    }
    

    Note that if the method passed as a string doesn't work, it will fail at runtime, not compile time, and crash your app. Be careful


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    Also, if your (Swift) class does not descend from an Objective-C class, then you must have a colon at the end of the target method name string and you must use the @objc property with your target method e.g.

    var rightButton = UIBarButtonItem(title: "Title", style: UIBarButtonItemStyle.Plain, target: self, action: Selector("method"))
    
    @objc func method() {
        // Something cool here   
    } 
    

    otherwise you will get a "Unrecognised Selector" error at runtime.


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    Swift 2.2+ and Swift 3 Update

    Use the new #selector expression, which eliminates the need to use string literals making usage less error-prone. For reference:

    Selector("keyboardDidHide:")
    

    becomes

    #selector(keyboardDidHide(_:))
    

    See also: Swift Evolution Proposal

    Note (Swift 4.0):

    If using #selectoryou would need to mark the function as @objc

    Example:

    @objc func something(_ sender: UIButton)


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    For future readers, I found that I experienced a problem and was getting an unrecognised selector sent to instance error that was caused by marking the target func as private.

    The func MUST be publicly visible to be called by an object with a reference to a selector.


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    Swift 4.0

    you create the Selector like below.

    1.add the event to a button like:

    button.addTarget(self, action: #selector(clickedButton(sender:)), for: UIControlEvents.touchUpInside)
    

    and the function will be like below:

    @objc func clickedButton(sender: AnyObject) {
    
    }
    

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    Just in case somebody else have the same problem I had with NSTimer where none of the other answers fixed the issue, is really important to mention that, if you are using a class that do not inherits from NSObject either directly or deep in the hierarchy(e.g. manually created swift files), none of the other answers will work even when is specified as follows:

    let timer = NSTimer(timeInterval: 1, target: self, selector: "test", 
                        userInfo: nil, repeats: false)
    func test () {}
    

    Without changing anything else other than just making the class inherit from NSObject I stopped getting the "Unrecognized selector" Error and got my logic working as expected.


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    If you want to pass a parameter to the function from the NSTimer then here is your solution:

    var somethingToPass = "It worked"
    
    let timer = NSTimer.scheduledTimerWithTimeInterval(0.01, target: self, selector: "tester:", userInfo: somethingToPass, repeats: false)
    
    func tester(timer: NSTimer)
    {
        let theStringToPrint = timer.userInfo as String
        println(theStringToPrint)
    }
    

    Include the colon in the selector text (tester:), and your parameter(s) go in userInfo.

    Your function should take NSTimer as a parameter. Then just extract userInfo to get the parameter that passed.


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    Selectors are an internal representation of a method name in Objective-C. In Objective-C "@selector(methodName)" would convert a source-code method into a data type of SEL. Since you can't use the @selector syntax in Swift (rickster is on point there), you have to manually specify the method name as a String object directly, or by passing a String object to the Selector type. Here is an example:

    var rightBarButton = UIBarButtonItem(
        title: "Logout", 
        style: UIBarButtonItemStyle.Plain, 
        target: self, 
        action:"logout"
    )
    

    or

    var rightBarButton = UIBarButtonItem(
        title: "Logout", 
        style: UIBarButtonItemStyle.Plain, 
        target: self, 
        action:Selector("logout")
    )
    

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    Swift 4.1
    With sample of tap gesture

    let gestureRecognizer = UITapGestureRecognizer()
    self.view.addGestureRecognizer(gestureRecognizer)
    gestureRecognizer.addTarget(self, action: #selector(self.dismiss(completion:)))
    
    // Use destination 'Class Name' directly, if you selector (function) is not in same class.
    //gestureRecognizer.addTarget(self, action: #selector(DestinationClass.dismiss(completion:)))
    
    
    @objc func dismiss(completion: (() -> Void)?) {
          self.dismiss(animated: true, completion: completion)
    }
    

    See Apple's document for more details about: Selector Expression


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    // for swift 2.2
    // version 1
    buttton.addTarget(self, action: #selector(ViewController.tappedButton), forControlEvents: .TouchUpInside)
    buttton.addTarget(self, action: #selector(ViewController.tappedButton2(_:)), forControlEvents: .TouchUpInside)
    
    // version 2
    buttton.addTarget(self, action: #selector(self.tappedButton), forControlEvents: .TouchUpInside)
    buttton.addTarget(self, action: #selector(self.tappedButton2(_:)), forControlEvents: .TouchUpInside)
    
    // version 3
    buttton.addTarget(self, action: #selector(tappedButton), forControlEvents: .TouchUpInside)
    buttton.addTarget(self, action: #selector(tappedButton2(_:)), forControlEvents: .TouchUpInside)
    
    func tappedButton() {
      print("tapped")
    }
    
    func tappedButton2(sender: UIButton) {
      print("tapped 2")
    }
    
    // swift 3.x
    button.addTarget(self, action: #selector(tappedButton(_:)), for: .touchUpInside)
    
    func tappedButton(_ sender: UIButton) {
      // tapped
    }
    
    button.addTarget(self, action: #selector(tappedButton(_:_:)), for: .touchUpInside)
    
    func tappedButton(_ sender: UIButton, _ event: UIEvent) {
      // tapped
    }
    

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    Create Refresh control using Selector method.   
        var refreshCntrl : UIRefreshControl!
        refreshCntrl = UIRefreshControl()
        refreshCntrl.tintColor = UIColor.whiteColor()
        refreshCntrl.attributedTitle = NSAttributedString(string: "Please Wait...")
        refreshCntrl.addTarget(self, action:"refreshControlValueChanged", forControlEvents: UIControlEvents.ValueChanged)
        atableView.addSubview(refreshCntrl)
    

    //Refresh Control Method

    func refreshControlValueChanged(){
        atableView.reloadData()
        refreshCntrl.endRefreshing()
    
    }
    

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    Since Swift 3.0 is published, it is even a little bit more subtle to declare a targetAction appropriate

    class MyCustomView : UIView {
    
        func addTapGestureRecognizer() {
    
            // the "_" is important
            let tapGestureRecognizer = UITapGestureRecognizer(target: self, action: #selector(MyCustomView.handleTapGesture(_:)))
            tapGestureRecognizer.numberOfTapsRequired = 1
            addGestureRecognizer(tapGestureRecognizer)
        }
    
        // since Swift 3.0 this "_" in the method implementation is very important to 
        // let the selector understand the targetAction
        func handleTapGesture(_ tapGesture : UITapGestureRecognizer) {
    
            if tapGesture.state == .ended {
                print("TapGesture detected")
            }
        }
    }
    

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    When using performSelector()

    /addtarget()/NStimer.scheduledTimerWithInterval() methods your method (matching the selector) should be marked as

    @objc
    For Swift 2.0:
        {  
            //...
            self.performSelector(“performMethod”, withObject: nil , afterDelay: 0.5)
            //...
    
    
        //...
        btnHome.addTarget(self, action: “buttonPressed:", forControlEvents: UIControlEvents.TouchUpInside)
        //...
    
        //...
         NSTimer.scheduledTimerWithTimeInterval(0.5, target: self, selector : “timerMethod”, userInfo: nil, repeats: false)
        //...
    
    }
    
    @objc private func performMethod() {
    …
    }
    @objc private func buttonPressed(sender:UIButton){
    ….
    }
    @objc private func timerMethod () {
    ….
    }
    

    For Swift 2.2, you need to write '#selector()' instead of string and selector name so the possibilities of spelling error and crash due to that will not be there anymore. Below is example

    self.performSelector(#selector(MyClass.performMethod), withObject: nil , afterDelay: 0.5)
    

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    you create the Selector like below.
    1.

    UIBarButtonItem(
        title: "Some Title",
        style: UIBarButtonItemStyle.Done,
        target: self,
        action: "flatButtonPressed"
    )
    

    2.

    flatButton.addTarget(self, action: "flatButtonPressed:", forControlEvents: UIControlEvents.TouchUpInside)
    

    Take note that the @selector syntax is gone and replaced with a simple String naming the method to call. There’s one area where we can all agree the verbosity got in the way. Of course, if we declared that there is a target method called flatButtonPressed: we better write one:

    func flatButtonPressed(sender: AnyObject) {
      NSLog("flatButtonPressed")
    }
    

    set the timer:

        var timer = NSTimer.scheduledTimerWithTimeInterval(1.0, 
                        target: self, 
                        selector: Selector("flatButtonPressed"), 
                        userInfo: userInfo, 
                        repeats: true)
        let mainLoop = NSRunLoop.mainRunLoop()  //1
        mainLoop.addTimer(timer, forMode: NSDefaultRunLoopMode) //2 this two line is optinal
    

    In order to be complete, here’s the flatButtonPressed

    func flatButtonPressed(timer: NSTimer) {
    }
    

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    I found many of these answers to be helpful but it wasn't clear how to do this with something that wasn't a button. I was adding a gesture recognizer to a UILabel in swift and struggled so here's what I found worked for me after reading everything above:

    let tapRecognizer = UITapGestureRecognizer(
                target: self,
                action: "labelTapped:")
    

    Where the "Selector" was declared as:

    func labelTapped(sender: UILabel) { }
    

    Note that it is public and that I am not using the Selector() syntax but it is possible to do this as well.

    let tapRecognizer = UITapGestureRecognizer(
                target: self,
                action: Selector("labelTapped:"))
    

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    Using #selector will check your code at compile time to make sure the method you want to call actually exists. Even better, if the method doesn’t exist, you’ll get a compile error: Xcode will refuse to build your app, thus banishing to oblivion another possible source of bugs.

    override func viewDidLoad() {
            super.viewDidLoad()
    
            navigationItem.rightBarButtonItem =
                UIBarButtonItem(barButtonSystemItem: .Add, target: self,
                                action: #selector(addNewFireflyRefernce))
        }
    
        func addNewFireflyReference() {
            gratuitousReferences.append("Curse your sudden but inevitable betrayal!")
        }
    

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    It may be useful to note where you setup the control that triggers the action matters.

    For example, I have found that when setting up a UIBarButtonItem, I had to create the button within viewDidLoad or else I would get an unrecognized selector exception.

    override func viewDidLoad() {
        super.viewDidLoad() 
    
        // add button
        let addButton = UIBarButtonItem(image: UIImage(named: "746-plus-circle.png"), style: UIBarButtonItemStyle.Plain, target: self, action: Selector("addAction:"))
        self.navigationItem.rightBarButtonItem = addButton
    }
    
    func addAction(send: AnyObject?) {     
        NSLog("addAction")
    }
    

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    Change as a simple string naming in the method calling for selector syntax

    var timer1 : NSTimer? = nil
    timer1= NSTimer(timeInterval: 0.1, target: self, selector: Selector("test"), userInfo: nil, repeats: true)
    

    After that, type func test().


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    For Swift 3

    //Sample code to create timer

    Timer.scheduledTimer(timeInterval: 1, target: self, selector: (#selector(updateTimer)), userInfo: nil, repeats: true)
    
    WHERE
    timeInterval:- Interval in which timer should fire like 1s, 10s, 100s etc. [Its value is in secs]
    target:- function which pointed to class. So here I am pointing to current class.
    selector:- function that will execute when timer fires.
    
    func updateTimer(){
        //Implemetation 
    } 
    
    repeats:- true/false specifies that timer should call again n again.
    

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    Selector in Swift 4:

    button.addTarget(self, action: #selector(buttonTapped(sender:)), for: UIControlEvents.touchUpInside)
    

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    For swift 3

    let timer = Timer.scheduledTimer(timeInterval: 0.01, target: self, selector: #selector(self.test), userInfo: nil, repeats: true)
    

    Function declaration In same class:

    @objc func test()
    {
        // my function
    }