> On 9 Mar 2016, at 21:32, Bill Cheeseman <wjcheese...@gmail.com> wrote:
>
> I am using storyboards in an OS X application written in Swift 2. It is a
> single window "shoebox" application that does not use NSDocument or Core
> Data. It is built with the Xcode 7.2.1 storyboard template, where the
> storyboard entry point is the main window controller scene and a "window
> content" relationship segue leads to the window's content view scene.
>
> In my AppDelegate class, I want to declare an instance property referring to
> the main window's content view controller. I need to refer to the content
> view controller because my AppDelegate provides programmatic content for one
> of the menu bar's menus and it needs to update a duplicate of that menu in a
> popup button in the content view. I anticipate needing a reference to the
> content view controller for other purposes, too, so I want to avoid
> duplicating code by putting it in an instance variable.
>
> It is of course impossible to set the property's value before the window's
> content view controller exists. The applicationDidFinishLaunching(_:)
> delegate method is apparently too early. If I set it there with
> 'mainContentViewController = NSApp.mainWindow!.contentViewController as!
> MainContentViewController', I get this fatal error at launch: "unexpectedly
> found nil while unwrapping an Optional value."
>
> I therefore set it using a lazy instance variable, like this:
>
> lazy var mainContentViewController: MainContentViewController = {
> NSApp.mainWindow!.contentViewController as! MainContentViewController
> }()
>
> This works fine -- but only if I take care to use the instance variable after
> the content view controller becomes available. My question is whether the
> following is a safe and sensible way to take care of the possibility that I
> might accidentally try to use it too early:
>
> lazy var mainContentViewController: MainContentViewController? = {
> guard let window = NSApp.mainWindow,
> let controller = window.contentViewController
> else {return nil}
> return controller as? MainContentViewController
> }()
>
> (I tried returning 'controller as! MainContentViewController', but I got this
> warning: "Treating a forced downcast to 'MainContentViewController' as
> optional will never produce 'nil'." I have to declare the variable as an
> Optional type because the guard statement might return nil.)
>
> —
just
return NSApp.mainWIndow?.contentViewController as?
MainContentViewController
works without all the guard and intermediate variables and still returns the
same optional.
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