[swift-users] How to do Cocoa bindings in Swift? IB rejects optionals

[David Sweeris]

Is `moc` declared in a non-"@objc" scope? I think there's a "@IBsomethingerather" that you have to put in front of those to let Interface Builder see them or something. Sorry I can't be more definitive, but I'm not in front of my computer and can't double-check.

HTH
- Dave Sweeris 

Sent from my iPhone

> On Jan 16, 2017, at 10:11, Jean-Denis Muys via swift-users <swift-users at swift.org> wrote:
> 
> Hi,
> 
> I am exploring the use of Swift for a Mac Cocoa application - using Xcode 8.2.1, and it seems I hit a roadblock regarding Cocoa bindings.
> 
> In this toy Core Data document-based project, I added an NSArrayController in the StoryBoard. I need to bind it a NSManagedObjectContext so that my user interface works by itself. I followed the solution outlined in Technical Q&A QA1871 (https://developer.apple.com/library/content/qa/qa1871/_index.html).
> 
> So I want to add a property of type ManagedObjectContext to my ViewController class. 
> 
> I naturally declared it as an optional:
> 
> var moc: ManagedObjectContext?
> 
> But when I enter the property name in the bindings inspector of InterfaceBuilder, it complains: there is a red exclamation mark, and hovering over it pops up this error message:
> 
> “The Managed Object Context binding expects to be bound to an object of type NSObject, but mac is of type ManagedObjectContext?”
> 
> And it fails at run time too.
> 
> changing the type to ManagedObjectContext! doesn’t help: IB complains in exactly the same way.
> 
> changing the type to a non optional ManagedObjectContext silences the IB error, but now my ViewController class doesn’t compile anymore. The error I get is:
> 
> class ViewController has no initialiser 
> 
> I completely understand this error message. And I can add an initialiser. But I get this new error message:
> 
> property ‘self.moc’ not initialised at super.init call.
> 
> I understand that one too, but what can I do? At initialiser-time, the managedObjectContext is not yet known. In Objective-C I would set it to nil, which I cannot do since the property is not an optional any more.
> 
> Do I really need to allocate a dummy sentinel ManagedObjectContext, just to make the compiler happy?
> 
> This would be ugly as hell, far worse than the nil value we use in Objective-C. Swift in that case, would not be safer, but less safe than Obj-C.
> 
> I find this idea repulsive. Or did I miss something?
> 
> Or is Swift fundamentally incompatible with Cocoa bindings? That would be a pity too.
> 
> Thanks,
> 
> Jean-Denis
> 
> 
> _______________________________________________
> swift-users mailing list
> swift-users at swift.org
> https://lists.swift.org/mailman/listinfo/swift-users