在Swift中将子类添加到UIView

Question

I am unable to add a subclass to my parent UIView class. I am trying to build a BOOK class and have various UIView and UIImageView classes to build the covers and the pages. I get an error when adding the subclass to SELF. Would love some insight. PS - total swift noob

//book
class bookview : UIView {

    var cover: UIView!
    var backcover: UIView!
    var page: UIImageView!

    init (pages: Int) {

        //backcover cover
        backcover = UIView(frame: CGRect(x: 200, y: 200, width: bookwidth, height: bookheight))
        backcover.backgroundColor = UIColor.blue
        self.addSubview(backcover)  //ERROR HERE

        //pages
        for i in 0 ..< pages {

            page = UIImageView(frame: CGRect(x: bookwidth * i/10, y: bookheight * i/10, width: bookwidth, height: bookheight))
            page.backgroundColor = UIColor.red
            self.addSubview(page)   //ERROR HERE

        }

        //front cover
        cover = UIView(frame: CGRect(x: 0, y: 0, width: bookwidth, height: bookheight))
        cover.backgroundColor = UIColor.blue
        self.addSubview(cover)   //ERROR HERE

        super.init(frame: CGRect(x: 0, y: 0, width: bookwidth, height: bookheight))


    }

    required init?(coder aDecoder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }

}


//add book
let book = bookview(pages: 3)

Answer 1

addSubview() is a method on UIView . UIView is your view's superclass. You cannot call methods on a superclass until it has been fully initialized.

To fix this, call super.init(frame:) earlier in your own init() function (before you call addSubview() ).

Answer 2

The issue is that you can't call methods on self in the initializer until there is a self to call them on. There is no established value for self until you have called the superclass initializer. In other words, how does a subclass of UIView know how to "addSubview" when it has not yet been initialized as a UIView yet?

So, in your code example, just move the line:

super.init(frame: CGRect(x: 0, y: 0, width: bookwidth, height: bookheight))

to be before any time you call self.addSubview()