“unexpectedly found nil” - delegate assignment in subVC

Question

I have been stuck on this for the past few days -

graphView is my UI Class instance - I declare my CalculatorViewDataSource protocol outside of the GraphView class, which contain weak var calcDataSource: CalculatorViewDataSource? in it.

in my GraphViewController, in the didSet{} of the graphView outlet I try to set the delegate to what I assume is an existing CalculatorViewController using the following code:

 if let vc = splitViewController?.viewControllers {
            println(vc)
            println(vc.count)
            if let fst = vc.first {
                println(fst.subviews)
                println(fst.subviews.first)
            }
        }
graphView.calcDataSource = splitViewController!.viewControllers.first!.subviews.first as CalculatorViewController

the code compile, but I crash with "unexpectedly found nil" when I get to the assignment of graphView.calcDataSource

(output)

[<UINavigationController: 0x7b71bd10>] 1 nil fatal error: unexpectedly found nil while unwrapping an Optional value

(storyboard)

SplitViewController - NavigationController - (Master) CalculatorViewController
     I
NavigationController - (Detail) GraphViewController`

• is the syntax or the assignment wrong?
• I am trying to delegate to the masterView of a UISplitView from the detail, should I try to set the delegate in the masterView? Does this assume the detail / graphView already exists? (this seem to be what ( errors creating a delegate from UISplitViewDetail to master in Swift ) hints at)

========

SOLVED!

I worked around this issue by working from inside prepareForSegue (with a storyboard segue on button called "Show Graph")

//CalculatorViewController.swift:
override func prepareForSegue(segue: UIStoryboardSegue?, sender: AnyObject!) {
    if (segue!.identifier == "Show Graph") {
        var yourNextViewController = (segue!.destinationViewController as UINavigationController)
        var detail = yourNextViewController.viewControllers[0] as GraphViewController
        var tempview = detail.view // FORCES THE VIEW object into existence, without this it will compile, but next line will crash at runtime (graphView nil)
        detail.graphView.calcDataSource = self
    }
}

note that var tempview = detail.view is critical here, despite not being used. I understand as it setting up the view and outlet..

Answer 1

How to (safely) unwrap optionals:

graphView.calcDataSource = splitViewController!.viewControllers.first!.subviews.first as CalculatorViewController

if let vc = splitViewController?.viewControllers {
    println(vc)
    if let fst = vc.first {
        println(fst.subviews)
        println(fst.subviews.first)
    }
}