Demonstration of using Core Data with SwiftUI

CoreDataList.swift

//
//  ContentView.swift
//  CoreDataSwiftUISample
//
//  Created by Eric Lewis on 8/8/19.
//  Copyright © 2019 Eric Lewis, Inc. All rights reserved.
//

import SwiftUI
import CoreData

extension FetchedResults where Result: Item {
    func delete(_ managedObjectContext: NSManagedObjectContext) -> (IndexSet) -> Void {
        func delete(_ offset: IndexSet) {
            var arr = Array(self)
            arr.remove(atOffsets: offset)
            
            let diff = arr.difference(from: self)
            for change in diff {
                switch change {
                case let .remove(_, element, _):
                    managedObjectContext.delete(element)
                case .insert(_, _, _):
                    print("nothing")
                }
            }
        }
        
        return delete
    }
    
    func move(_ managedObjectContext: NSManagedObjectContext) -> (IndexSet, Int) -> Void {
        func move(_ offset: IndexSet, _ destination: Int) {
            managedObjectContext.perform {
                var arr = Array(self)
                arr.move(fromOffsets: offset, toOffset: destination)
                for i in 0..<arr.count {
                    arr[i].order = Int32(i)
                }
            }
        }
        
        return move
    }
}

extension Item {
    var checkbox: String {
        isComplete ? "checkmark.square.fill" : "square"
    }
    
    var checkboxColor: Color {
        isComplete ? .green : .secondary
    }
}

struct Cell: View {
    @Environment(\.managedObjectContext) var managedObjectContext
    @ObservedObject var item: Item
    
    init(_ item: Item) {
        self.item = item
    }
    
    func toggleComplete() {
        managedObjectContext.perform {
            self.item.objectWillChange.send()
            self.item.isComplete.toggle()
            try? self.managedObjectContext.save()
        }
    }
    
    var body: some View {
        Button(action: toggleComplete) {
            HStack {
                Image(systemName: item.checkbox)
                    .foregroundColor(item.checkboxColor)
                Text(item.title ?? "")
            }
        }
    }
}

struct ContentView: View {
    @Environment(\.managedObjectContext) var managedObjectContext
    @FetchRequest(fetchRequest: listFetchRequest) var items: FetchedResults<Item>

    func add() {
        let item = Item(context: self.managedObjectContext)
        item.title = "Test \(items.count)"
        item.order = Int32(items.count)
    }

    var body: some View {
        NavigationView {
            List {
                ForEach(items, id: \.objectID) { item in
                    Cell(item)
                }
                .onDelete(perform: items.delete(managedObjectContext))
                .onMove(perform: items.move(managedObjectContext))
            }
            .navigationBarTitle("List")
            .navigationBarItems(leading: EditButton(), trailing:
                Button(action: add) {
                    Image(systemName: "plus")
                }
            )
        }
    }
    
    static var listFetchRequest: NSFetchRequest<Item> {
        let request: NSFetchRequest<Item> = Item.fetchRequest()
        request.sortDescriptors = [NSSortDescriptor(key: "order", ascending: true)]
          
        return request
    }
}