書籍の詳細を表示しています
Showing book details

import SwiftUI
import CoreData

struct DetailView: View {
    let book: Book
    
    var body: some View {
        GeometryReader { geometry in
            VStack {
                ZStack(alignment: .bottomTrailing) {
                    Image(self.book.genre ?? "Fantasy")
                        .frame(maxWidth: geometry.size.width)

                    Text(self.book.genre?.uppercased() ?? "FANTASY")
                        .font(.caption)
                        .fontWeight(.black)
                        .padding(8)
                        .foregroundColor(.white)
                        .background(Color.black.opacity(0.75))
                        .clipShape(Capsule())
                        .offset(x: -5, y: -5)
                }
                Text(self.book.author ?? "Unknown author")
                    .font(.title)
                    .foregroundColor(.secondary)

                Text(self.book.review ?? "No review")
                    .padding()

                RatingView(rating: .constant(Int(self.book.rating)))
                    .font(.largeTitle)

                Spacer()
            }
            
        }
        .navigationBarTitle(Text(book.title ?? "Unknown Book"), displayMode: .inline)
    }
}

struct DetailView_Previews: PreviewProvider {
    static let moc = NSManagedObjectContext(concurrencyType: .mainQueueConcurrencyType)

    static var previews: some View {
        let book = Book(context: moc)
        book.title = "Test book"
        book.author = "Test author"
        book.genre = "Fantasy"
        book.rating = 4
        book.review = "This was a great book; I really enjoyed it."

        return NavigationView {
            DetailView(book: book)
        }
    }
}

NSSortDescriptorによるフェッチ要求のソート
Sorting fetch requests with NSSortDescriptor

struct ContentView: View {
@Environment(\.managedObjectContext) var moc
//@FetchRequest(entity: Book.entity(), sortDescriptors: []) var books: FetchedResults<Book>
//@FetchRequest(entity: Book.entity(), sortDescriptors: [NSSortDescriptor(keyPath: \Book.title, ascending: true)]) var books: FetchedResults<Book>
    
@FetchRequest(entity: Book.entity(), sortDescriptors: [
    NSSortDescriptor(keyPath: \Book.title, ascending: true),
    NSSortDescriptor(keyPath: \Book.author, ascending: true)
]) var books: FetchedResults<Book>
    
@State private var showingAddScreen = false
    
    
    var body: some View {

コアデータフェッチリクエストからの削除
Deleting from a Core Data fetch request

import SwiftUI
import CoreData

struct ContentView: View {
    @Environment(\.managedObjectContext) var moc
    //@FetchRequest(entity: Book.entity(), sortDescriptors: []) var books: FetchedResults
    //@FetchRequest(entity: Book.entity(), sortDescriptors: [NSSortDescriptor(keyPath: \Book.title, ascending: true)]) var books: FetchedResults
        
    @FetchRequest(entity: Book.entity(), sortDescriptors: [
        NSSortDescriptor(keyPath: \Book.title, ascending: true),
        NSSortDescriptor(keyPath: \Book.author, ascending: true)
    ]) var books: FetchedResults
    
    //---------------------------------
    func deleteBooks(at offsets: IndexSet) {
        for offset in offsets {
            // find this book in our fetch request
            let book = books[offset]

            // delete it from the context
            moc.delete(book)
        }

        // save the context
        try? moc.save()
    }
    
@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")) {
                    NavigationLink(destination: DetailView(book: book)) {
                        EmojiRatingView(rating: book.rating)
                            .font(.largeTitle)

                        VStack(alignment: .leading) {
                            Text(book.title ?? "Unknown Title")
                                .font(.headline)
                            Text(book.author ?? "Unknown Author")
                                .foregroundColor(.secondary)
                        }
                    }
                }.onDelete(perform: deleteBooks)
            }
            .navigationBarTitle("Bookworm")
            //.navigationBarItems(trailing: Button(action: {
            .navigationBarItems(leading: EditButton(), 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)

    }
}

アラートを使用してプログラムでNavigationLinkをポップする
Using an alert to pop a NavigationLink programmatically

import SwiftUI
import CoreData

struct DetailView: View {
    let book: Book
    
    @Environment(\.managedObjectContext) var moc
    @Environment(\.presentationMode) var presentationMode
    @State private var showingDeleteAlert = false
    
    func deleteBook() {
        moc.delete(book)

        // uncomment this line if you want to make the deletion permanent
        // try? self.moc.save()
        presentationMode.wrappedValue.dismiss()
    }
    
    var body: some View {
        GeometryReader { geometry in
            VStack {
                ZStack(alignment: .bottomTrailing) {
                    Image(self.book.genre ?? "Fantasy")
                        .frame(maxWidth: geometry.size.width)

                    Text(self.book.genre?.uppercased() ?? "FANTASY")
                        .font(.caption)
                        .fontWeight(.black)
                        .padding(8)
                        .foregroundColor(.white)
                        .background(Color.black.opacity(0.75))
                        .clipShape(Capsule())
                        .offset(x: -5, y: -5)
                }
                Text(self.book.author ?? "Unknown author")
                    .font(.title)
                    .foregroundColor(.secondary)

                Text(self.book.review ?? "No review")
                    .padding()

                RatingView(rating: .constant(Int(self.book.rating)))
                    .font(.largeTitle)

                Spacer()
            }
            
        }
        .navigationBarTitle(Text(book.title ?? "Unknown Book"), displayMode: .inline)
        .alert(isPresented: $showingDeleteAlert) {
            Alert(title: Text("Delete book"), message: Text("Are you sure?"), primaryButton: .destructive(Text("Delete")) {
                    self.deleteBook()
                }, secondaryButton: .cancel()
            )
        }
        .navigationBarItems(trailing: Button(action: {
            self.showingDeleteAlert = true
        }) {
            Image(systemName: "trash")
        })
    }
}

struct DetailView_Previews: PreviewProvider {
    static let moc = NSManagedObjectContext(concurrencyType: .mainQueueConcurrencyType)

    static var previews: some View {
        let book = Book(context: moc)
        book.title = "Test book"
        book.author = "Test author"
        book.genre = "Fantasy"
        book.rating = 4
        book.review = "This was a great book; I really enjoyed it."

        return NavigationView {
            DetailView(book: book)
        }
    }
}