Loading a view makes the program crash - xcode

Question

I'm still learning how the view works, but I found a problem that I couldn't solve...
I got the class GraficsBalancGlobalViewControllerwhich is subclass of the class GraficViewController
class GraficsBalancGlobalViewController: GraficViewController {
#IBAction func afegeixGrafic(sender: NSButton) {
addNewGrafic() // which is set on the GraficViewController
}
}
And when I perform the IBAction afegeixGrafic my program crashes on the line marked below:
class GraficViewController: NSViewController, GraficViewDataSource {
#IBAction func button(sender: NSButton) {
addNewGrafic()
}
func addNewGrafic() {
let frame = NSRect(x: 0, y: 0, width: self.view.bounds.width , height: self.view.bounds.width * 0.25)
let nouGrafic = GraficView(frame: frame)
scrollView.addSubview(nouGrafic) <---- BREAK here!
}
#IBOutlet weak var scrollView: NSView!
//...more code
}
The compiler says that:
fatal error: unexpectedly found nil while unwrapping an Optional value
but the button (IBAction) inside the GraficViewController works well!! So i suppose that the problem is related with the scrollView, but I have no idea of what can be.. It is initialized..
just to mention that the GraficView(frame: frame)is not the problem because I try it and works well.

Answer 1

I do believe ! is the culprit of your woes:
#IBOutlet weak var scrollView: NSView!
Xcode does generate this entry with force unwrap (!) for IBOutlets, but it should really be an optional (?) because you have no guaranties when that reference is going to be set. If you have some logic that depend on scrollView's existence, you can do so by relying on didSet:
#IBOutlet weak var scrollView: NSView? {
didSet {
guard let sview = scrollView else {
return // because scrollView is nil for some reason
}
// do your scrollView existence dependent logic here (eg. reload content)
}
}
func addNewGrafic() {
let frame = NSRect(x: 0, y: 0, width: self.view.bounds.width , height: self.view.bounds.width * 0.25)
let nouGrafic = GraficView(frame: frame)
scrollView?.addSubview(nouGrafic)
}
I hope this helps.