Implementing Objective-C protocol in Swift class

Question

I have a comprehension question. I want to use the Dropbox Objective-C framework in an iOS Swift app.
I already imported the framework successfully and set the import clause in the bridging header.
I was also able to run the authorization process so I think the framework works.
Then I try to use a component of the framework which is declared as protocol:

class ViewController: UIViewController, DBRestClientDelegate {
}

I sat the delegate property, called the loadMetadata method and implemented the corresponding event function:

let dbRestClient = DBRestClient(DBSession.shared())
dbRestClient.delegate = self
dbRestClient.loadMetadata("/")
...

func restClient(client: DBRestClient!, loadedMetadata metadata: DBMetadata!) {
}

What I'm wondering is that it seems not necessary to implement all methods of that protocol. Is this correct? In Swift implementing only a part of a protocol is enough?
I ask because the compiler displays no errors but the delegation method is never called.

Answer 1

Generally, in Swift you have to implement ALL methods of a protocol. (See this question about optional protocol methods: How to define optional methods in Swift protocol?)

But as you said, the framework is written in Objective-C. Objective-C supports optional methods in protocols.

@protocol ProtocolName
@required
// list of required methods
@optional
// list of optional methods
@end

Source

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That's why you don't necessarily need to implement all methods declared in a protocol. Usually, only the most important methods are marked with @required, because when calling an optional method, you should always check, if the delegate implemented it.