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Xcode – How do I hide Apple's delegate functions in my class from outside users of my class?

I have the following class:

class Scanner: NSObject, AVCaptureVideoDataOutputSampleBufferDelegate {}

It has a delegate method implemented in the class from AVCaptureVideoDataOutputSampleBufferDelegate:

func captureOutput(_ output: AVCaptureOutput, didOutput sampleBuffer: CMSampleBuffer, from connection: AVCaptureConnection)
    {}

Even when I set the function to private, fileprivate, or internal, it still appears in the code-complete in Xcode:

enter image description here

Is there a way to hide this call from outside class use?

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2

Answers


  1. 0

    One way is to create a private inner class that conforms to the protocol, and have the inner class hold a weak reference to the outer class, in case you need to use members from the outer class in the implementation of the delegate method.

    class Scanner {
    ...

    private class VideoOutputDelegate: NSObject, AVCaptureVideoDataOutputSampleBufferDelegate {
        weak var scanner: Scanner?
        init(scanner: Scanner) { self.scanner = scanner }

        func captureOutput(_ output: AVCaptureOutput, didOutput sampleBuffer: CMSampleBuffer, from connection: AVCaptureConnection) {
            ...
        }
    }

    private let videoOutputDelegate = VideoOutputDelegate(scanner: self)
}

    Rather than setting the sampleBufferDelegate to self, you can set it to videoOutputDelegate instead.

    (I think), AVCaptureVideoDataOutput holds a weak reference to its sampleBufferDelegate, so videoOutputDelegate here is the only strong reference here that is keeping the object alive.

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  2. 0

    Your problem is somewhat related to the Single Responsibility Principle. Basically your class tries to do one more task than needed – reacting to AVFoundation events, in this case the captureOutput method.

    Recommending to split your class in two, have one class that handles all the AVFoundation setup/delegate, and have Scanner only deal with raw data. This way:

    • you keep the concerns separated, which allows you to reuse the Scanner in other contexts too
    • you might even be able to remove the AVFoundation dependency from the scanner, making it more independent
    • you don’t get the undesired functionality, as yes, a scanner doesn’t need to expose AVFoundation delegate methods.

    Also, most likely your scanner doesn’t need a AVCaptureConnection to do its work, but unfortunately this dependency is leaked into the class due to the delegate. And splitting the responsibilities helps with this problem too.

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