迅速：推迟非可选对象的初始化

Question

When dialing with CocoaTouch, it often happens that UIView(Controller) subclass properties can't be initialized in init method (ex. we need view already loaded), but logically they are non-optional and even non-var. In such cases the property must be optional to compile without errors, what looks pretty ugly - the code is fulfilled with ! .

Is there any way to solve this problem? I would imagine some deferred initialization. Perfectly if such property can compile without initial value and crash at runtime if it's accessed prior to be initialized.

Some code sample to describe the issue:

class MyVC: UIViewController {
    @IBOutlet var someLabel: UILabel!
    let viewBasedParam: CustomClass // how to keep it non-optional if it can be initialized after view has been loaded?

    override func viewDidLoad() {
        super.viewDidLoad()
        self.viewBasedParam = CustomClass(self.someLabel.text)
    }
}

PS CustomClass can't have default initializer, because it requires data from view.

Answer 1

In your MyVC you can have a convenience init method where you can initialize the let variables. Try this and let me know if it works for you:

class MyVC: UIViewController {
let viewBasedParam: CustomClass

    convenience init() {
        self.init(nibName:nil, bundle:nil)
        self.viewBasedParam = CustomClass(self.someLabel.text)//else just initialize with empty string here and then assign actual value in viewDidLoad
    }
}

Answer 2

As far as I've discovered the workaround solution may be following:

class MyVC: UIViewController {
    @IBOutlet var someLabel: UILabel!
    private var _viewBasedParam: CustomClass? = nil
    var viewBasedParam: CustomClass {
        get { return self._viewBasedParam! } // always unwrap private optional
        set { self._viewBasedParam = newValue }
    }

    override func viewDidLoad() {
        super.viewDidLoad()
        self.viewBasedParam = CustomClass(self.someLabel.text)
    }
}