When developing for a platform that utilizes several languages, like iOS, it is important to be able to bridge the gap between the languages. In particular, when building apps that are written in both Swift and Objective-C, one must be able to bridge the gap between protocols defined in Swift and Objective-C. In this post, we will look at the basics of bridging between Swift protocols and Objective-C.
Objective-C protocols (often times referred to as "delegates") are a powerful tool when it comes to handling communication between objects. Similarly, in Swift, we use protocols to specify the behavior that is expected from an object when we want to pass an instance of a class to another class. When we use protocols to define the expected behavior between objects, the objects can then communicate easily and efficiently.
When creating an architecture for a hybrid iOS app written in both Swift and Objective-C, we need to bridge the gap between the two languages. Luckily, this process can be simplified by taking advantage of the Objective-C runtime.
If an Objective-C protocol has been declared in your project, you can reference it in Swift by simply prepending it with an @objc. This will generate an automatically bridged proxy object in Swift which works precisely like its Objective-C counterpart. You can now use the Objective-C protocol in your Swift code. As an example, the following code defines an Objective-C protocol that takes a callback as a parameter:
@protocol MyProtocol
- (void)callbackWithData:(id)data;
@end
In Swift, you can reference this protocol by simply prepending it with an @objc:
@objc protocol MyProtocol {
func callbackWithData(data: Any!)
}
The resulting Swift protocol will behave exactly like the Objective-C protocol and can be used to communicate between objects written in Swift and Objective-C. This process can be used for other types of bridging operations, such as bridging classes and enums.
Bridging the gap between Objective-C and Swift is an important consideration for iOS developers. Taking advantage of the Objective-C runtime to bridge protocols and other types between the two languages is a simple and effective way to build hybrid apps that are written in Swift and Objective-C.