Where to initialize in Swift?

Question

I have a very general question about the Initialization in Swift. Unlike in Objective C it's now possible to call the init() directly at the declaration outside of my functions: e.g.

class ViewController: UIViewController {
    let myView: UIView = UIView()

    override func viewDidLoad() {
        super.viewDidLoad()

        myView.frame = getFrame()
        myView.backgroundColor = UIColor.redColor()
        self.view.addSubview(myView)

    }

    func getFrame() -> CGRect {
        return CGRectMake(0, 0, 100, 100)
    }
}

In Objective C I would have done the initialization in my function.

But what if I want to call an Initializer with parameters which are not set yet? e.g. I want to init with a frame which is being calculated in a func()

class ViewController: UIViewController {

    //THIS IS NOT WOKRING
    let myView: UIView = UIView(frame: getFrame())

    override func viewDidLoad() {
        super.viewDidLoad()

        myView.backgroundColor = UIColor.redColor()
        self.view.addSubview(myView)

    }

    func getFrame() -> CGRect {
        return CGRectMake(0, 0, 100, 100)
    }
}

I don't wanna do my initializations at two different places in the Code. Is there any general pattern for the initializations?

Answer 1

So your options for initialisation in swift are numerous. With your current example you cannot use the method getFrame() yet because you do not yet have a reference to self as the ViewController has not get been initialised. Instead you could use:

let myView: UIView = UIView(frame: CGRectMake(0, 0, 100, 100))

As this does not require the reference to self. Alternatively you could lazy instantiation which will get run after self is available (this can only be used with var not let:

lazy var myView: UIView = {
    return UIView(frame:self.getFrame())
}()

To answer your question, when using UIKit class where you often don't have control over their instantiation you can keep doing it the same was as you were in objective c and use implicitly unwrapped optionals (to prevent you having to use a ! or ? every time you instantiate a variable, e.g.:

var myView: UIView!

override func viewDidLoad(){
    super.viewDidLoad();

    myView = UIView(frame:getFrame())
}

This however does not work with let constants, as they need to be assigned either immediately or in the constructor of the object. Hope this helps.