Function to pause my AR session and clear variables and anchors

Question

I'm trying to create a function that pauses AR session and also clears my dictionary variable entityDictionaries and removes all anchors. However, I'm kinda stuck and don't know how to start.

Here is a code for my main view:

    struct InitiateARView: View {
    @StateObject var vm = ARPreparationViewModel()
     
    var body: some View {
        VStack {
             if vm.isLoading {
                 Button("Start", action: {
                     vm.prepareAR()
                 })
                 
             } else {
                 ZStack {
                     ARExperience()
                         .edgesIgnoringSafeArea(.all)
                     VStack {
                         HStack {
                             Spacer()
                             Button("Stop AR", action: {
                                // Call to clear AR session function here
                             })
                         }
                         Spacer()
                     }
                 }
             }  
         }
     }
}

And here is simplified version of my ARExperience struct

struct ARExperience: UIViewRepresentable {
    var arView = ARView(frame: .zero) 
    
    var entityDictionaries = [String: (anchor: AnchorEntity, model: ModelEntity)]()
    
    func makeCoordinator() -> Coordinator {
        Coordinator(parent: self)
    }
    
    class Coordinator: NSObject, ARSessionDelegate {
        var parent: ARExperience
    
        init(parent: ARExperience) {
            self.parent = parent
        }
        
        func session(_ session: ARSession, didAdd anchors: [ARAnchor]) {
            guard let validAnchor = anchors[0] as? ARImageAnchor else { return }
            let anchor = AnchorEntity(anchor: validAnchor)
            let videoPlane = createdVideoPlayerNodeFor(validAnchor.referenceImage)
            anchor.addChild(videoPlane)
            parent.arView.scene.addAnchor(anchor)
            if let targetName = validAnchor.referenceImage.name {
                parent.entityDictionaries[targetName] = (anchor, videoPlane)
            }
        }

        func session(_ session: ARSession, didUpdate anchors: [ARAnchor]) {

        }
        
    }

    func makeUIView(context: Context) -> ARView {
        //...        
    }
    
    func updateUIView(_ uiView: ARView, context: Context) {

    }
}

Any help that can get me 'unstuck' with this problem will be perfect

Any of these may be relevant in terms of how to communicate from SwiftUI to the represented view: https://stackoverflow.com/questions/70958776/perform-scnaction-using-a-button-swiftui https://stackoverflow.com/questions/69442079/pause-a-spritekit-scene-from-swiftui-using-spriteviewispaused-without-reinit https://stackoverflow.com/questions/66619751/complex-uikit-swiftui-interface-via-uiviewcontrollerrepresentable — jnpdx, Jun 03 '23 at 14:38
You've got some basic mistakes, StateObject isn't designed for view model objects you need to learn the View struct. And then you'll realise Coordinator(parent: self) is a bug because self is a value not an object. — malhal, Jun 04 '23 at 13:52

lorem ipsum · Accepted Answer · 2023-06-03T23:42:42.323

One way to do it is to separate UIKit from SwiftUI and have a Common source of truth where the 2 frameworks can communicate with each other.

struct InitiateARView: View {
    @StateObject var vm = ARPreparationViewModel()
    
    var body: some View {
        VStack {
            if vm.isLoading {
                Button("Start", action: {
                    vm.prepareAR()
                })
                
            } else {
                ZStack {
                    ARExperience_UI(vm: vm) //Your experiece would change to include the shared VM
                        .edgesIgnoringSafeArea(.all)
                    VStack {
                        HStack {
                            Spacer()
                            Button("Stop AR", action: {
                                //Make SwiftUI changes
                                vm.clearAR() // Then you can access UIKit via the VM
                            })
                        }
                        Spacer()
                    }
                }
            }
        }
    }
}

The shared source of truth would look something like.

//Works with both SwiftUI and UIKit
class ARPreparationViewModel: ObservableObject{
    //reference to UIKit, will be nil until set by ViewController init.
    @Published var vc: ARExperienceVC?
    @Published var isLoading: Bool = false
    
    deinit {
        vc = nil
    }
    
    func prepareAR() {
        guard let vc = vc else {
            print("Missing View Controller")
            return
        }
        vc.prepareAR()
    }
    func clearAR() {
        guard let vc = vc else {
            print("Missing View Controller")
            return
        }
        //Make any source of truth changes
        vc.clearAR()
    }
}

Then the UIViewControllerRepresentable code would be simplified to just create the new UIViewController, this just serves as a bridge.

// SwiftUI
struct ARExperience_UI: UIViewControllerRepresentable { //Change to a UIViewControllerRepresentable
    let vm: ARPreparationViewModel
    
    func makeUIViewController(context: Context) -> some UIViewController {
        ARExperienceVC(vm: vm) // Create the new ViewController with all the UIKit Code
    }
    func updateUIViewController(_ uiViewController: UIViewControllerType, context: Context) {
        
    }
}

The UIKit code does the heavy lifting.

// Keep UIKit code here
class ARExperienceVC: UIViewController {
    let vm: ARPreparationViewModel

    lazy var arView: ARView = {
        let arView = ARView(frame: .zero)
        arView.session.delegate = self
        
        return arView
    }()
    
    init(vm: ARPreparationViewModel) {
        self.vm = vm
        super.init(nibName: nil, bundle: nil)
        self.vm.vc = self //Without this the source of truth won't have access to the ViewController
    }
    
    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
    
    deinit {
        self.vm.vc = nil
    }
    
    override func viewDidLoad() {
        super.viewDidLoad()
        view.addSubview(arView)
        arView.pinToSuperview(self.view) // This lest SwiftUI control the size because the view will be attached to the bordering anchors.
    }
    
    func prepareAR() {
        print("\(type(of: self)) :: \(#function)")
    }
    func clearAR() {
        print("\(type(of: self)) :: \(#function)")
        //Make UIKit changes.
    }
}

extension ARExperienceVC: ARSessionDelegate {
    func session(_ session: ARSession, didAdd anchors: [ARAnchor]) {
        
    }

    func session(_ session: ARSession, didUpdate anchors: [ARAnchor]) {

    }
}

extension UIView{
    func pinToSuperview(_ superView: UIView){
        self.translatesAutoresizingMaskIntoConstraints = false
        self.topAnchor.constraint(equalTo: superView.topAnchor).isActive = true
        self.bottomAnchor.constraint(equalTo: superView.bottomAnchor).isActive = true
        self.leadingAnchor.constraint(equalTo: superView.leadingAnchor).isActive = true
        self.trailingAnchor.constraint(equalTo: superView.trailingAnchor).isActive = true
    }
}

Function to pause my AR session and clear variables and anchors

1 Answers1