loadNibNamed returns the view, not "the view"?

Question

I have a small xib, Teste.xib

owned by TesteView

class TesteView: UIView {
    @IBOutlet var tf:UITextField!
    @IBOutlet var sw:UISwitch!
    }

Now, we're gonna load it (and for example stuff it in a stack view).

let t:TesteView = TesteView()
let v = Bundle.main.loadNibNamed("Teste", owner: t, options: nil)?[0] as! UIView
v.heightAnchor.constraint(equalToConstant: 200).isActive = true
stack?.insertArrangedSubview(v, at: 3)

in fact, that's fine.

Everything works.

But note that you insert "v", not "t". "v" is not "the TesteView", it's just some damned view that is floating around.

If you do the following,

t.heightAnchor.constraint(equalToConstant: 200).isActive = true
stack?.insertArrangedSubview(t, at: 3)

it is meaningless, that doesn't work.

But t "is" the view, it's a UIView (indeed, it is a TesteView). It should be the thing you insert.

So you have to use the "two different" things ...

t.tf.text = "WTF???"
// use "t" for that sort of thing
v.heightAnchor.constraint(equalToConstant: 200).isActive = true
v.backgroundColor = UIColor.blue
// but use "v" for that sort of thing
stack?.insertArrangedSubview(v, at: 3)

It seems weird that "t" and "v" are not the same.

(Indeed, should TesteView even have been a subclass of UIView? Maybe it should be something else - just a plain class?? It seems one can not really use it as a view so WTF is it??)

What's the deal on this and/or what is the usual idiom?

NOTE ...

nowadays, there is no reason to ever do this. Just use a small UIViewController. For decades everyone said "Why doesn't apple let you simply load a view controller by id?", well now you can. No problems:

    let t = self.storyboard?.instantiateViewController(withIdentifier: "TesteID") as! Teste
    t.view.heightAnchor.constraint(equalToConstant: 200).isActive = true
    stack?.insertArrangedSubview(t.view, at: 3)
    t.tex.text = "WTH???"

probably, you don't want to use the custom class for the _File's Owner_, but for the view's itself. — holex, Jan 14 '17 at 16:05
you can connect the outlets to the _View_ not to the _File's Owner_, but the procedure is excetly the same. — holex, Jan 14 '17 at 16:08
@JoeBlow, in your code you need to use the correct xib's name (e.g. `TesteView`) when you load it from nib. — holex, Jan 14 '17 at 16:19

matt · Accepted Answer · 2017-01-14T17:28:36.723

This code makes no sense; your use of t is pointless:

let t:TesteView = TesteView()
let v = Bundle.main.loadNibNamed("Teste", owner: t, options: nil)?[0] as! UIView

The object of nominating an owner is to provide some already existing instance with properties that match outlets in the nib. This allows the outlets to be used, and the views to which they lead can immediately be referred to by name.

That is what happens when a view controller / view pair is loaded from a storyboard, and is why storyboards work the way they do. The view nib is loaded with the view controller as owner. So if the view nib has outlet mySwitch and the view controller has outlet property mySwitch, they match up and the term self.mySwitch can be used by the view controller instance to refer to the switch.

You can arrange the same thing yourself when loading a .xib file. But you are not doing that; your code is just deliberately silly.

For example (this is from my book, and you can download and run the example for yourself):

class ViewController: UIViewController {
    @IBOutlet var coolview : UIView!
    override func viewDidLoad() {
        super.viewDidLoad()
        Bundle.main.loadNibNamed("View", owner: self)
        self.view.addSubview(self.coolview)
    }
}

If you have configured View.xib with its File's Owner proxy's class set to ViewController, and if you've then drawn an outlet from the File's Owner to the view and named that outlet coolview, when we load it is matched with the coolview property and the last line works — we can refer to the nib-loaded view as self.coolview.

And notice, please, that we never had to capture the result of loading the nib as an array of views and then refer to element zero of that array, as you do. The view gets slotted right into the name coolview. That is how you load a nib so as to get a useful name or names.

Sorry about that. My point is only that you wouldn't _make_ a UIView _in code_ just to add as a "mop" to access the outlets and then throw that UIView away, as you do. You've "stacked the deck" by deliberately making a silly example. In _my_ example, the owner already exists. — matt, Jan 14 '17 at 18:56
And I totally don't agree about "nowadays". I use _xib_ files all the time. Storyboards are another tool in the toolbox but they didn't drive out any of my other tools. — matt, Jan 14 '17 at 18:56
If that's really true, maybe you'll read my online book, which explains all this: http://www.apeth.com/iOSBook/ch07.html#_nib_loading_and_file_8217_s_owner — matt, Jan 14 '17 at 20:01
But that's problematic too; you should not be using a view controller to do "dumpster diving" into a nib. You can't just arbitrarily throw a view controller's view into the interface. — matt, Jan 14 '17 at 20:40

loadNibNamed returns the view, not "the view"?

NOTE ...

1 Answers1