Hidden subviews in UIViewController

Question

Take this code:

class ViewController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()
        var i = 0
        //let v1 = UIView(frame:CGRectMake(113, 111, 132, 194))
        //v1.backgroundColor = UIColor.redColor()
        //self.view.addSubview(v1)

        for v in self.view.subviews as! [UIView] {
            v.removeFromSuperview()
            i++
        }
        println(i)
    }
}

The for loop removes all subviews from the superview. At the end of the loop, i is 2, meaning there were 2 subviews removed. Since I didn't add any myself, what are these subviews?

Answer 1

There are two hidden layers in default UIViewController. When you print the output of your code you'll find

<_UILayoutGuide: 0x7f981a513750; frame = (0 0; 0 0); hidden = YES; layer = > <_UILayoutGuide: 0x7f981a5142f0; frame = (0 0; 0 0); hidden = YES; layer = >

Answer 2

A UIViewController's view property can have some internal subviews used by the system, and these can vary based on iOS version, context, etc. If you want to remove a subview that you yourself created, one simple way to do this is to declare your v1 UIView as a property of your ViewController class

class ViewController: UIViewController {

    let v1 = UIView(frame:CGRectMake(113, 111, 132, 194))

    override func viewDidLoad() {
        super.viewDidLoad()

        //add the view
        v1.backgroundColor = UIColor.redColor()
        self.view.addSubview(v1)

        //remove the view
        v1.removeFromSuperview()
    }
}