Checking out drag n' drop in Swift UI

Dnd.swift

import SwiftUI

struct AnimalView: View {
    var model: Animal

    var body: some View {
        VStack {
            Image(systemName: model.systemImageName)
                .resizable()
                .scaledToFit()
                .frame(width: 50, height: 50)

            Text(model.name)
        }
        .onDrag {
            NSItemProvider(object: self.model)
        }
    }
}

struct TrashView: View {
    @EnvironmentObject var zoo: Zoo

    var body: some View {
        Image(systemName: "trash")
            .resizable()
            .scaledToFit()
            .frame(width: 100, height: 100)
            .onDrop(of: [Animal.typeIdentifier], isTargeted: nil) { ips in

                guard let ip = ips.first(where: { ip in ip.hasItemConformingToTypeIdentifier(Animal.typeIdentifier) }) else { return false }

                ip.loadObject(ofClass: Animal.self) { reading, _ in
                    guard let animal = reading as? Animal else { return }
                    DispatchQueue.main.async {
                        self.zoo.amimals.removeAll(where: { a in a.name == animal.name })
                    }
                }
                return true
            }
    }
}

struct ContentView: View {
    @ObservedObject var zoo = Zoo()

    var body: some View {
        HStack {
            Spacer()
            VStack {
                ForEach(zoo.amimals, id: \.name) { animal in
                    AnimalView(model: animal)
                }
            }
            Spacer()
            TrashView().environmentObject(zoo)
        }
    }
}

struct ContentView_Previews: PreviewProvider {
    static var previews: some View {
        ContentView()
    }
}

// MARK: - Model

class Zoo: ObservableObject {
    @Published var amimals = [
        Animal(name: "Hare", systemImageName: "hare.fill"),
        Animal(name: "Ant", systemImageName: "ant.fill"),
        Animal(name: "Tortoise", systemImageName: "tortoise.fill"),
    ]
}

final class Animal: NSObject {
    public static let typeIdentifier = "dnd.animal"

    let name: String
    let systemImageName: String

    internal init(name: String, systemImageName: String) {
        self.name = name
        self.systemImageName = systemImageName
    }
}

extension Animal: NSItemProviderReading {
    static var readableTypeIdentifiersForItemProvider: [String] = [typeIdentifier]

    static func object(withItemProviderData data: Data, typeIdentifier: String) throws -> Animal {
        let components = String(data: data, encoding: .utf8)!.split(separator: ",").map(String.init)
        return Animal(name: components[0], systemImageName: components[1])
    }
}

extension Animal: NSItemProviderWriting {
    static var writableTypeIdentifiersForItemProvider: [String] = [typeIdentifier]

    func loadData(withTypeIdentifier typeIdentifier: String, forItemProviderCompletionHandler completionHandler: @escaping (Data?, Error?) -> Void) -> Progress? {
        completionHandler("\(name),\(systemImageName)".data(using: .utf8), nil) // very terrible encoding and decoding 🙃
        let p = Progress(totalUnitCount: 1)
        p.completedUnitCount = 1
        return p
    }
}

I copied and pasted the code as-is and ran it. However, it does not work. The guard at line 32 fails because the ips array is empty. Can you please advise?
guard let ip = ips.first(where:... <-- ips is empty

What if you try to do an if let ip = ips.first...

Hi juandahurt, Thanks for the reply.
As it turns out, I came back to the project after a couple of days, and now the "ips" parameter variable is populated correctly and the code works. I did not change any code, so I cannot explain why it was not working earlier. All good now. :-)

To any future people reading this, this example doesn't work building for macOS Big Sur, Xcode 12.5. You have to add "dnd.animal" as a UTType in your info.plist, you can see how to do that here.

Alternatively, you can just remove the "dnd.animal" and just swap it with a different UTType, I used "UTType.data" and everything worked ok

static let typeIdentifier = UTType.data
static var readableTypeIdentifiersForItemProvider: [String] = [typeIdentifier.identifier]
static var writableTypeIdentifiersForItemProvider: [String] = [typeIdentifier.identifier]