SwiftUI UIViewRepresentable 和自定义委托

Question

When creating a UIViewControllerRepresentable for SwiftUI, how do you create a Coordinator so that it can access the delegate of a third party library?

In this case, I am trying to access BBMetal , a photo-filtering library.

This is a truncated version of the code we are trying to 'bridge' to SwiftUI:

class CameraPhotoFilterVC: UIViewController {
    private var camera: BBMetalCamera!
    private var metalView: BBMetalView!
    private var faceView: UIView!

    override func viewDidLoad() {
        super.viewDidLoad()
        ...

    }

    override func viewDidAppear(_ animated: Bool) {
        super.viewDidAppear(animated)
        camera.start()
    }...
}

extension CameraPhotoFilterVC: BBMetalCameraPhotoDelegate {
    func camera(_ camera: BBMetalCamera, didOutput texture: MTLTexture) {
        // do something with the photo
    }

    func camera(_ camera: BBMetalCamera, didFail error: Error) {
        // In main thread
        print("Fail taking photo. Error: \(error)")
    }
}

Using UIViewRepresentable everything sets up properly and the CameraPhotoFilterVC works, starts up the camera, etc, but the extension does not respond. We tried to set this up as a Coordinator:

func makeCoordinator() -> Coordinator {
 Coordinator(self)
}

func makeUIViewController(context: UIViewControllerRepresentableContext<CameraPreviewView>) -> CameraViewController {
 let cameraViewController = CameraViewController()
 // Throws an error because what we really want is a BBMetalCameraPhotoDelegate
 //cameraViewController.delegate = context.coordinator
 return cameraViewController
}

class Coordinator: NSObject, BBMetalCameraPhotoDelegate {
 var parent: CameraPreviewView
 init(_ parent: CameraPreviewView) {
  self.parent = parent
 }

 func camera(_ camera: BBMetalCamera, didOutput texture: MTLTexture) {
  print("do something with the photo")
 }
 func camera(_ camera: BBMetalCamera, didFail error: Error) {
  print("Fail taking photo. Error: \(error)")
 }
}

We also tried simply leaving an extension of the ViewController:

final class CameraViewController : UIViewController  {
...
}

extension CameraViewController: BBMetalCameraPhotoDelegate {
   func camera(_ camera: BBMetalCamera, didOutput texture: MTLTexture) {
        ...
}

However the delegate methods from BBMetalCameraPhotoDelegate do not 'fire.

I suppose the question is: in UIViewControllerRepresentable or UIViewRepresentable, how do you add an "external" delegate in the makeUIViewController method?

Usually, if this was say a UIPickerView, the following line would work:

picker.delegate = context.coordinator

But in this case the delegate is 'once removed'

Answer 1

You need to set the BBMetalCamera 's delegate at some point before you use it.

You might do it immediately after creating it. You didn't show how you create it, so I don't know if that would be a good place to set it.

You could probably just do it in viewDidLoad :

override func viewDidLoad() {
    super.viewDidLoad()

    camera.photoDelegate = self
}