Using Swift protocols in Objective-C
Sep 3, 2014 ·
I’m currently creating two games for iOS. One is made in Swift & SpriteKit, while one is in Objective-C & UIKit. I now want to share logic by using my Swift protocols in Objective-C.
The good part
The apps share an Objective-C core library and use CoreMeta to bootstrap each app and select which implementation to use for a certain protocol.
Objective-C protocols in the library work great in Swift. To implement them in Swift, I just add them to my bridging header and implement them.
For instance, the Animal protocol is implemented by an AnimalView UIView in Objective-C & UIKit, while Swift & SpriteKit has an AnimalNode that inherits SKNode.
The bad part
All in all, Swift is a really nice experience. Less code, easier to read - I love it! However, as I created the Swift protocol and tried to register it with CoreMeta, I ran into problems.
CoreMeta is written in Objective-C, which lets you pass in protocols as parameters, which you with the @protocol(ProtocolName) syntax. In Swift, you use ProtocolName.self.
This works great for Objective-C protocols, but not at all for Swift protocols. Swift protocols can’t be cast to Protocol *, and thus can’t be used as method parameter with CoreMeta.
The solution
To use Swift protocols in Objective-C, just add @objc before the protocol keyword. After this, I could use bootstrap them with CoreMeta as I do with the Objective-C protocols.
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