Cannot convert value of type 'NSObject -> () -> PostFeed' to expected argument type 'AnyObject?'

Question

I'm adding a UISwitch in the following way:

  let anonSwitch : UISwitch = {
   let mySwitch = UISwitch()
    mySwitch.on = false
    mySwitch.setOn(false, animated: false);
    mySwitch.tintColor = UIColor(red: (69/255.0), green: (209/255.0), blue: (153/255.0), alpha: 1.0)
    mySwitch.addTarget(self, action: #selector(handleAnonSwitch), forControlEvents: .ValueChanged)

    return mySwitch
}()

Now I'm getting the following error message on the self keyword in mySwitch.addTarget :

 Cannot convert value of type 'NSObject -> () -> PostFeed' to expected argument type 'AnyObject?'

I use self in all my other addTarget functions for UIButton and I never encounter this error

Answer 1

Change your let into a lazy var .

I'm not sure exactly what the compiler is thinking (or where its crazy error message is coming from), but my guess is this:

In Swift, variables which are let have to be initialized before you can use self . One reason for this is that the compiler can't verify that addTarget(action:forControlEvents:) isn't going to try to call anonSwitch() on whatever it gets for target , or do something else, like access a different variable that would be initialized after anonSwitch , that depends on initialization having completed for this object.

Using lazy var means that the compiler can verify that the value assigned to anonSwitch won't be accessed before self is a valid object, because it won't be possible to call anonSwitch until all other members of the class have been initialized.