Your Second iOS & SwiftUI App

Nov 4 2021 · Swift 5.5, iOS 15, Xcode 13

Part 3: Managing Rows

23. Environment

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Previous episode: 22. Challenge: New Book Sheet Next episode: 24. Environment Values

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Coming off of that challenge, ready to go with a view that allows for creation of a book, let’s write a method that will add that new book to our library.

  var sortedBooks: [Book] { booksCache }

  func addNewBook(_ book: Book)

  /// An in-memory cache of the manually-sorted books that are persistently stored.

  func addNewBook(_ book: Book, image: Image?) {

  }

  var sortedBooks: [Book] { booksCache }

  /// <#Description#>
  /// - Parameters:
  ///   - book: <#book description#>
  ///   - image: <#image description#>
  func addNewBook(_ book: Book, image: UIImage?) {
    booksCache.insert(book, at: 0)
    uiImages[book] = image
  }

  var sortedBooks: [Book] { booksCache }

  /// <#Description#>
  func addNewBook(_ book: Book, image: UIImage?) {

  var sortedBooks: [Book] { booksCache }

  /// Adds a new book at the start of the library's manually-sorted books.
  func addNewBook(_ book: Book, image: Image?) {

  func addNewBook(_ book: Book, image: UIImage?) {
    booksCache.insert(book, at: 0)
  }

    booksCache.insert(book, at: 0)
    uiImages[book] = image
  }

mutating func addNewBook(_ book: Book, image: UIImage?) {

class Library {

  var sortedBooks: [Book] { booksCache }

  func addNewBook(_ book: Book, image: UIImage?) {

class Library: ObservableObject {

@Published private var booksCache: [Book] = [

@Published var uiImages: [Book: UIImage] = [:]

    .padding()
    .toolbar {

    }
  }

    .toolbar {
      ToolbarItem(placement: <#T##ToolbarItemPlacement#>, content: <#T##() -> _#>)
    }

    .toolbar {
      ToolbarItem(placement: .status) {

      }
    }

        ToolbarItem(placement: .status) {
          Button("Add to Library") {

          }
        }

  var body: some View {
    NavigationView {
      VStack(spacing: 24) {

      .padding()
      .navigationTitle("Got a new book?")
      .toolbar {

  @State var image: UIImage? = nil
  @ObservedObject var library: Library

  var body: some View {

@EnvironmentObject var library: Library

      trailing: Button("Add") {
        library.addNewBook(book, image: image)
      }

NewBookView().environmentObject(<#T##object: ObservableObject##ObservableObject#>)

NewBookView().environmentObject(Library())

struct ContentView: View {
  @State var addingNewBook = false
  @EnvironmentObject var library: Library

  var body: some View {

struct ContentView_Previews: PreviewProvider {
  static var previews: some View {
    ContentView()
      .environmentObject(Library())
      .previewedInAllColorSchemes
  }
}

    ContentView()
      .environmentObject(Library())
      .previewedInAllColorSchemes

    ContentView()
      .environmentObject(Library())

ContentView()

ContentView().environmentObject(Library())

  @ObservedObject var book: Book
  @EnvironmentObject var library: Library

  var body: some View {

  static var previews: some View {
    DetailView(book: .init())
      .environmentObject(Library())
      .previewedInAllColorSchemes
  }

ReviewAndImageStack(book: book, image: $library.images[book])

destination: DetailView(book: book)

  @ObservedObject var book: Book
  @EnvironmentObject var library: Library

  var body: some View {

uiImage: library.images[book],

        ForEach(library.sortedBooks) { book in
          BookRow(book: book)
        }