APTargets

If you've ever seen this error...

-[MyProject.ViewController buttonTapped]: unrecognized selector sent to instance 0x7f9b42d48ae0

...then congratulations, you're an iOS developer.

We all hate selectors, and now you can eliminate them for good.

Usage

UIControl+Target.swift

After importing UIControl+Target.swift into your project, you'll have a new method exposed for adding targets:

addTarget(forControlEvents: UIControlEvents, action: () -> Void)

This method allows you to add a target to any UIControl (such as a UIButton), and define the closure in-place. With Xcode's auto formatting, this is what your target might look like:

myButton.addTarget(.TouchUpInside) { () -> Void in
    print("This gets called when I tap the button!")
}

But of course, this is Swift and we can lose the () -> Void in for a much cleaner version:

myButton.addTarget(.TouchUpInside) {
    print("This gets called when I tap the button!")
}

Important note: Just like all closures in Swift, you must be careful not to create reference cycles.

How could this create a reference cycle?

Suppose we have a UIViewController which owns a UIButton (a common scenario). The following code would create a reference cycle, causing the view controller to remain in memory after its dismissal:

override func viewDidLoad() {
    myButton.addTarget(.TouchUpInside) {
        print("This gets called when I tap the button!")
        self.counter += 1
    }
}

Referencing self (the view controller), or any property or method of self, within the closure will cause a reference cycle to occur.

How to prevent reference cycles

Luckily, this is very easy to avoid. If you need to access a UIControl's parent within the the target, you can simply make the parent unowned:

myButton.addTarget(.TouchUpInside) {[unowned self]() in
    print("This gets called when I tap the button!")
    self.counter += 1
}

That's not so bad, right? But there's an even better way:

myButton.addTarget(.TouchUpInside) {[unowned self] in self.buttonTapped()}

Where somewhere you've defined the function:

func buttonTapped() {
    print("This gets called when I tap the button!")
    self.counter += 1
}

This method is preferable because it avoids defining large blocks of code within the viewDidLoad method in your view controller.

Useful code snippet

Sometimes we get lazy, so here's a code snippet that you can install in Xcode for perfect autocompletion every time:

addTarget(<#UIControlEvents#>) {[unowned self] in self.<#method#>}

Returning sender

With UIControls, you often need the control itself to be returned as sender to your target method. Just like with standard selectors, this is also supported with APTargets:

myButton.addTarget(.TouchUpInside) {[unowned self] in self.printTitle(self.myButton)}

Where your method accepts the button as a parameter:

func printTitle(sender: UIButton) {
    print(sender.titleLabel?.title)
}

The caveat is that you must explicitly define sender (in this case, the button) while adding the target. Still a lot better than the old-fashioned way!

Advantages

Using APTargets, you no longer need to pass strings as selectors to UIControl targets.

Why is that so great?

No more uncaught typos, no more mismatched function names, and finally proper compiler checks! You'll never see this error ever again:

unrecognized selector sent to instance...

Give it a shot - you'll never go back!