What is the correct way of accessing a Swift Delegate from Objective-C?

Question

Environment: Xcode 6.1.1 & Xcode 6.2 Beta

Greetings:
I need to publish a NSString within a Swift doc from a neighboring Objective-C doc within the same project. For example, display "Hello World" generated in Objective-C upon a Swift page.
I've made a proof-of-concept demo; based on feedback.

I'm thinking of using an ObjC --> Swift delegate via a protocol pattern as shown below:

Note: the Swift file is the delegate.

Here I'm calling the delegate method in Swift, from Objective-C:

#pragma mark - Action methods
- (IBAction)sendDelegateAction:(UIButton *)sender {
    [_delegate radiusString:@"Hello World"];
}

I've instantiated the Objective-C file to link the delegate to the instance (I hope I got it right):

let geo32Controller = MyObjCTableViewController()
geo32Controller.delegate = self

So far, the compiler complained that the Swift protocol couldn't be found.
Here's the protocol (declared in Swift):

@objc protocol DiscoveryContributeProtocol {
    // optional
    func radiusString(radiusString:String)
}

And here's the delegate reference to that protocol in the Objective-C header file:

@interface MyObjCTableViewController : UIViewController<UITableViewDelegate, UITableViewDataSource>
@property (nonatomic, weak) id<DiscoveryContributeProtocol> delegate;
@end

However, the compiler can't find the protocol:

---

BTW: when I put the bridge reference in the ObjC's header file, I get a compiler error:

Two Questions:

1. Do I have the correct pattern (did I instantiate the ObjC correctly) ?
   
2. How do I make the Objective-C portion see the Swift protocol for the delegate link?

Answer 1

You have the right idea, but have a few bugs that are preventing this from working.

1. You've declared Geo32Boundaries as conforming to the DiscoveryContributeProtocol, but it doesn't need to and doesn't actually implement it, it only has a property that conforms to that protocol. That's the source of the "Method 'radiusString:' not implemented" error:

   @interface Geo32Boundaries: UIViewController    // <-- that's all you need
   

2. You're setting the delegate incorrectly -- the code you have there looks like it's trying to set a class instance of Geo32Boundaries to self, but you're also trying to call it like a function. You'll need to set the delegate on a the instance of the Geo32Boundaries view controller that is being presented to the user. I don't know where that code lives, so I can't give a great example, but it'll be something like:

   geo32Controller.delegate = self
   

3. Lastly, though not a bug, your protocol should really be called DiscoveryContributeDelegate -- we usually don't use "protocol" in the protocol name.