[Mac OS] Custom Copy / Paste with Swift UI Transferable + support for NSPasteboard (NSPasteboardWriting, NSPasteboardReading) and drag / drop

transferable-item.png

TransferableItem.swift

//
//  TransferableItem.swift
//
//  Created by Gboyega Dada on 22/11/2023.
//
// @see https://stackoverflow.com/a/57648296/1661299
// @see https://exploringswift.com/blog/creating-a-nsitemprovider-for-custom-model-class-drag-drop-api
// @see https://stackoverflow.com/a/66169874/1661299
//

import Foundation
import SwiftUI
import UniformTypeIdentifiers


final class TransferableItem: NSObject, Identifiable, Codable {
    var id: String = UUID().uuidString
    
    let name: String
    let email: String
    
    init(name: String, email: String) {
        self.name = name
        self.email = email
    }
    
    convenience init?(pasteboardPropertyList propertyList: Any, ofType type: NSPasteboard.PasteboardType) {
        guard let data = propertyList as? Data,
            let instance = try? PropertyListDecoder().decode(TransferableItem.self, from: data) else { return nil }
        
        self.init(name: instance.name, email: instance.email)
    }
}

extension TransferableItem {
    static func == (lhs: TransferableItem, rhs: TransferableItem) -> Bool {
         return
            lhs.id == rhs.id &&
            lhs.name == rhs.name &&
            lhs.email == rhs.email
     }
    
    override func isEqual(_ object: Any?) -> Bool {
        guard let other = object as? TransferableItem else {
            return false
        }
        
        return id == other.id &&
                name == other.name &&
                email == other.email
    }
    
    override var hash: Int {
        var hasher = Hasher()
        hasher.combine(id)
        hasher.combine(name)
        hasher.combine(email)
        
        return hasher.finalize()
    }
}

extension TransferableItem: Transferable {
    static var transferRepresentation: some TransferRepresentation {
        DataRepresentation(contentType: .transferableItem) { item in
            try PropertyListEncoder().encode(item)
        } importing: { data in
            try PropertyListDecoder().decode(TransferableItem.self, from: data)
        }
        
        /// ⚠️ Draggable won't work without this ⚠️
        DataRepresentation(contentType: .data) { item in
            try PropertyListEncoder().encode(item)
        } importing: { data in
            try PropertyListDecoder().decode(TransferableItem.self, from: data)
        }
    }
}

extension TransferableItem: NSPasteboardWriting, NSPasteboardReading  {

    public func writingOptions(forType type: NSPasteboard.PasteboardType, pasteboard: NSPasteboard) -> NSPasteboard.WritingOptions {
        return .promised
    }
    
    public func writableTypes(for pasteboard: NSPasteboard) -> [NSPasteboard.PasteboardType] {
        return [.transferableItem]
    }
    
    public func pasteboardPropertyList(forType type: NSPasteboard.PasteboardType) -> Any? {
        if type == .transferableItem {
            return try? PropertyListEncoder().encode(self)
        }
        return nil
    }
    
    static func readableTypes(for pasteboard: NSPasteboard) -> [NSPasteboard.PasteboardType] {
        return [.transferableItem]
    }
    
    public static func readingOptions(forType type: NSPasteboard.PasteboardType, pasteboard: NSPasteboard) -> NSPasteboard.ReadingOptions {
        return .asData
    }
}


extension UTType {
    static var transferableItem: UTType { UTType(exportedAs: "com.example.MyApp.TransferableItem") }
}

extension NSPasteboard.PasteboardType {
    static var transferableItem = NSPasteboard.PasteboardType("com.example.MyApp.TransferableItem")
}

TransferableItemExampleView.swift

//
//  USAGE
//  -----------------------------------------
//  TransferableItemExampleView.swift
//
//  Created by Gboyega Dada on 24/11/2023.
//

import SwiftUI

struct TransferableItemExampleView: View {
    @State var listItems: [TransferableItem] = [
        TransferableItem(name: "Sam", email: "[email protected]"),
        TransferableItem(name: "Quorra", email: "[email protected]"),
        TransferableItem(name: "Kevin", email: "[email protected]"),
        TransferableItem(name: "Tron", email: "[email protected]"),
        TransferableItem(name: "Zuse", email: "[email protected]"),
        TransferableItem(name: "Gem", email: "[email protected]"),
    ]
    @State var selected: Set<TransferableItem> = []
    
    /// For toolbar  copy / paste buttons
    private let nspasteboard = NSPasteboard.general
    
    var body: some View {
        VStack(alignment: .leading) {
            Text("My Copyable Items")
                .font(.title2)
            
            List(listItems) { item in
                Label(item.name, systemImage: "person")
                
                /// Draggable !
                .draggable(item) {
                    Text(item.name) // Preview
                }
            }
            
            /// This will work with system pasteboard COPY command
            .copyable(Array(selected))
            
            /// This will work with system pasteboard CUT command
            .cuttable(for: TransferableItem.self) {
               for item in selected {
                   listItems.removeAll(where: { $0 == item })
               }
               return Array(selected)
            }
            
            /// This will work with system pasteboard PASTE command
            .pasteDestination(for: TransferableItem.self) { values in
                listItems.append(contentsOf: values)
            } validator: { values in
                values.filter { !$0.name.isEmpty }
            }
        }
        
        /// This allows you drop transferable items into the list
        .dropDestination(for: TransferableItem.self) { values, location in
            listItems.append(contentsOf: values)
            
            return true
        } isTargeted: { isTargeted in
            // Highlight target e.t.c
        }
        
        /// For copy / paste buttons in your toolbar, you may need to use NSPasteboard directly
        .toolbar {
            Button("Copy Selected Items") {
                /// @see https://developer.apple.com/forums/thread/730619
                nspasteboard.prepareForNewContents()
                nspasteboard.writeObjects(Array(selected))
            }
            .disabled(selected.count == 0)
            
            Button("Cut Selected Items") {
                for item in selected {
                    listItems.removeAll(where: { $0 == item })
                }
                
                /// @see https://developer.apple.com/forums/thread/730619
                nspasteboard.prepareForNewContents()
                nspasteboard.writeObjects(Array(selected))
            }
            .disabled(selected.count == 0)
            
            Button {
                guard let values = nspasteboard.readObjects(forClasses: [TransferableItem.self]) as? [TransferableItem] else { return }
                
                listItems.append(contentsOf: values)
            } label: {
                Label("Paste Items", systemImage: "doc.on.clipboard")
            }
            .disabled(!nspasteboard.canReadObject(forClasses: [TransferableItem.self]))
        }
    }
}

#Preview {
    TransferableItemExampleView()
}

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