Core Dataで本を作成する
Creating books with Core Data

最初のタスクは、本のコアデータモデルを設計し、次にデータベースに本を追加するための新しいビューを作成することです。

Bookworm.xcdatamodeld追加作業にて、
新たに、Book追加した段階でerror有り。
一旦、削除し新たに作成してOKとなる。

import SwiftUI

struct AddBookView: View {
    @Environment(\.managedObjectContext) var moc
    
    @State private var title = ""
    @State private var author = ""
    @State private var rating = 3
    @State private var genre = ""
    @State private var review = ""
    
    let genres = ["Fantasy", "Horror", "Kids", "Mystery", "Poetry", "Romance", "Thriller"]
    
    @Environment(\.presentationMode) var presentationMode
    
    var body: some View {
       NavigationView {
            Form {
                Section {
                    TextField("Name of book", text: $title)
                    TextField("Author's name", text: $author)

                    Picker("Genre", selection: $genre) {
                        ForEach(genres, id: \.self) {
                            Text($0)
                        }
                    }
                }

                Section {
                    Picker("Rating", selection: $rating) {
                        ForEach(0..<6) {
                            Text("\($0)")
                        }
                    }

                    TextField("Write a review", text: $review)
                }

                Section {
                    Button("Save") {
                        // add the book
                        let newBook = Book(context: self.moc)
                        newBook.title = self.title
                        newBook.author = self.author
                        newBook.rating = Int16(self.rating)
                        newBook.genre = self.genre
                        newBook.review = self.review
                        try? self.moc.save()

                        self.presentationMode.wrappedValue.dismiss()
                    }
                }
            }
            .navigationBarTitle("Add Book")
        }
    }
}

struct AddBookView_Previews: PreviewProvider {
    static var previews: some View {
        let context = (UIApplication.shared.delegate as! AppDelegate).persistentContainer.viewContext
        return AddBookView().environment(\.managedObjectContext, context)

    }
}

import SwiftUI
import CoreData

struct ContentView: View {
@Environment(\.managedObjectContext) var moc
@FetchRequest(entity: Book.entity(), sortDescriptors: []) var books: FetchedResults<Book>

@State private var showingAddScreen = false
    
    
    var body: some View {
        NavigationView {
            Text("Count: \(books.count)")
                .navigationBarTitle("Bookworm")
                .navigationBarItems(trailing: Button(action: {
                    self.showingAddScreen.toggle()
                }) {
                    Image(systemName: "plus")
                })
                .sheet(isPresented: $showingAddScreen) {
                    AddBookView().environment(\.managedObjectContext, self.moc)
                }
        }
    }
}

struct ContentView_Previews: PreviewProvider {
    static var previews: some View {
        let context = (UIApplication.shared.delegate as! AppDelegate).persistentContainer.viewContext
        return ContentView().environment(\.managedObjectContext, context)

    }
}

カスタムの星評価コンポーネントの追加
Adding a custom star rating component

import SwiftUI

struct RatingView: View {
    @Binding var rating: Int

    var label = ""

    var maximumRating = 5

    var offImage: Image?
    var onImage = Image(systemName: "star.fill")

    var offColor = Color.gray
    var onColor = Color.yellow
    
    func image(for number: Int) -> Image {
        if number > rating {
            return offImage ?? onImage
        } else {
            return onImage
        }
    }
    
    var body: some View {
        HStack {
            if label.isEmpty == false {
                Text(label)
            }

            ForEach(1..<maximumRating + 1) { number in
                self.image(for: number)
                    .foregroundColor(number > self.rating ? self.offColor : self.onColor)
                    .onTapGesture {
                        self.rating = number
                    }
            }
        }
    }
}


struct RatingView_Previews: PreviewProvider {
    static var previews: some View {
        RatingView(rating: .constant(4))
    }
}

@FetchRequestでリストを作成する
Building a list with @FetchRequest

SwiftUIを使用すると、カスタムUIコンポーネントを簡単に作成できます。これは、これらのコンポーネントが実質的には@Binding、私たちが読むために公開された一種のビューにすぎないためです。

これを実証するために、ユーザーが画像をタップして1から5までのスコアを入力できる星評価ビューを作成します。

import SwiftUI

struct EmojiRatingView: View {
    let rating: Int16

    var body: some View {
        switch rating {
        case 1:
            return Text("1")
        case 2:
            return Text("2")
        case 3:
            return Text("3")
        case 4:
            return Text("4")
        default:
            return Text("5")
        }
    }
}

struct EmojiRatingView_Previews: PreviewProvider {
    static var previews: some View {
        EmojiRatingView(rating: 3)
    }
}

import SwiftUI
import CoreData

struct ContentView: View {
@Environment(\.managedObjectContext) var moc
@FetchRequest(entity: Book.entity(), sortDescriptors: []) var books: FetchedResults<Book>

@State private var showingAddScreen = false
    
    
    var body: some View {
        NavigationView {
            //Text("Count: \(books.count)")
            List {
                ForEach(books, id: \.self) { book in
                    NavigationLink(destination: Text(book.title ?? "Unknown Title")) {
                        EmojiRatingView(rating: book.rating)
                            .font(.largeTitle)

                        VStack(alignment: .leading) {
                            Text(book.title ?? "Unknown Title")
                                .font(.headline)
                            Text(book.author ?? "Unknown Author")
                                .foregroundColor(.secondary)
                        }
                    }
                }
            }
            .navigationBarTitle("Bookworm")
            .navigationBarItems(trailing: Button(action: {
                self.showingAddScreen.toggle()
            }) {
                Image(systemName: "plus")
            })
            .sheet(isPresented: $showingAddScreen) {
                AddBookView().environment(\.managedObjectContext, self.moc)
            }
        }
    }
}

struct ContentView_Previews: PreviewProvider {
    static var previews: some View {
        let context = (UIApplication.shared.delegate as! AppDelegate).persistentContainer.viewContext
        return ContentView().environment(\.managedObjectContext, context)

    }書籍の詳細を表示しています
}