Core data for favourite buttons - ios

Question

I want to make it so you can favourite a "landmark" in one view (LandmarkDetail), and access a list of all the "landmarks" in another view with the ones I've favourited highlighted. First I used "#AppStorrage" but I was told too to use Core Data for it instead. So far I have the favourite button working in the LandmarkDetail view with "#AppStorage" but apparently I need to change that so it uses Core Data.
I've look around to get an understanding of how to do it with Core Data but I could really use a helping hand if anyone can help. I've already seen and read some tutorials about core data and how to set it up, but I can't find anything for my specific problem where I pull in data from a JSON and I need Core Data to handle the favourite feature.
Here is my code for the favourite button
struct FavoriteButton: View {
#AppStorage ("isFavorite") var isFavorite: Bool = false
var body: some View {
Button {
isFavorite.toggle()
} label: {
Label("Toggle Favorite", systemImage: isFavorite ? "star.fill" : "star")
.labelStyle(.iconOnly)
.foregroundColor(isFavorite ? .yellow : .gray)
}
}
}
Code from the landmark detail view
struct LandmarkDetail: View {
var body: some View {
ScrollView {
VStack(alignment: .leading) {
HStack {
Text(landmark.name)
.font(.title)
FavoriteButton()
}
}
}
}
}
Code for the rows in the list view
This is the one not working yet, so far it just pulls the data from a JSON.
MODEL
import Foundation
import SwiftUI
import CoreLocation
struct Landmark: Hashable, Codable, Identifiable {
var id: Int
var name: String
var park: String
var state: String
var description: String
var isFavorite: Bool
var isFeatured: Bool
var category: Category
enum Category: String, CaseIterable, Codable {
case lakes = "Lakes"
case rivers = "Rivers"
case mountains = "Mountains"
}
private var imageName: String
var image: Image{
Image(imageName)
}
var featureImage: Image? {
isFeatured ? Image(imageName + "_feature") : nil
}
private var coordinates: Coordinates
var locationCoordinate: CLLocationCoordinate2D {
CLLocationCoordinate2D(
latitude: coordinates.latitude,
longitude: coordinates.longitude)
}
struct Coordinates: Hashable, Codable {
var latitude: Double
var longitude: Double
}
}
import Foundation
import Combine
final class ModelData: ObservableObject {
#Published var landmarks: [Landmark] = load("landmarkData.json")
var hikes: [Hike] = load("hikeData.json")
#Published var profile = Profile.default
var features: [Landmark] {
landmarks.filter { $0.isFeatured }
}
var categories: [String: [Landmark]] {
Dictionary(
grouping: landmarks,
by: { $0.category.rawValue }
)
}
}
func load<T: Decodable>(_ filename: String) -> T {
let data: Data
guard let file = Bundle.main.url(forResource: filename, withExtension: nil)
else {
fatalError("Couldn't find \(filename) in main bundle.")
}
do {
data = try Data(contentsOf: file)
} catch {
fatalError("Couldn't load \(filename) from main bundle:\n\(error)")
}
do {
let decoder = JSONDecoder()
return try decoder.decode(T.self, from: data)
} catch {
fatalError("Couldn't parse \(filename) as \(T.self):\n\(error)")
}
}

Answer 1

First of all you need to create a .xcdatamodeld file named Landmarks. You can create it by pressing right button on the principal folder of your project and searching Data Model. After you need to create a new Entity named Landmark. You can add attributes showed in your model like id, name, park, etc... with their types. After you need to create a new Swift file in which you can create you Core Data Controller like this:
class DataController: ObservableObject {
let container = NSPersistentContainer(name: "Landmarks")
init() {
container.loadPersistentStores { description, error in
if let error = error {
print("Core Data failed to load: \(error.localizedDescription)")
}
}
}
}
Successively, you need to add to your LandmarksApp.swift file the following code:
struct LandmarksApp: App {
#StateObject private var dataController = DataController()
var body: some Scene {
WindowGroup {
ContentView()
.environment(\.managedObjectContext, dataController.container.viewContext)
}
}
}
Continue adding this to your LandmarkDetail view:
struct LandmarkDetail: View {
#Environment(\.managedObjectContext) var moc
var body: some View {
ScrollView {
VStack(alignment: .leading) {
HStack {
Text(landmark.name)
.font(.title)
FavoriteButton()
}
}
}
}
}
To create a new item and add to Core Data you can write:
let landmark = Landmark(context: moc)
landmark.id = id
landmark.name = name
landmark.park = park
etc...
try? moc.save()
For your JSON data you can create a function that convert all JSON data in Core Data following these steps.