I'm creating a view programatically, and adding a function so the action responds to the UIControlEvents.TouchUpInside event:
button.addTarget(self, action: action, forControlEvents: UIControlEvents.TouchUpInside)
So, by going into the documentation I've added this action as a selector:
#selector(ViewController.onRegularClick)
XCode then complaints about:
Argument of #selector refers to a method that is not exposed to Objective-C
So I have to set up the handler function with:
@objc func onRegularClick(sender: UIButton)
Can some one please put this noob on the right direction by guiding me to the documentation, or even give a short explanation, on:
Thank you!
- why can't I no longer pass simply the function name String to the action?
Using strings for selectors has been deprecated, and you should now write #selector(methodName)
instead of "methodName"
. If the methodName() method doesn't exist, you'll get a compile error – another whole class of bugs eliminated at compile time. This was not possible with strings.
- how is the proper way to implement this following the Swift Way? Using the Selector class?
You did it the right way:
button.addTarget(self, action: #selector(ClassName.methodName(_:)), forControlEvents: UIControlEvents.TouchUpInside)
- why do we need to pass the @objc keyword and how it affects the function?
In Swift the normal approach is to bind method's calls and method's bodies at compile time (like C and C++ do). Objective C does it at run time. So in Objective C you can do some things that are not possible in Swift - for example it is possible to exchange method's implementation at run time (it is called method swizzling). Cocoa was designed to work with Objective C approach and this is why you have to inform the compiler that your Swift method should be compiled in Objective-C-like style. If your class inherits NSObject it will be compiled ObjC-like style even without @objc keyword.
When there are some arguments in the method, you should declare the selector as:
let selector = #selector(YourClass.selector(_:))
You can type only #selector(selector(_:))
if the selector is in the same class of the caller. _:
means that accept one parameter. So, if it accept more parameters, you should do something like: (_:, _:)
and so on.
I found out that the @objc
is needed only when the function is declared as private or the object doesn't inherit from NSObject
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