#EnvironmentObject property not working properly in swiftUI - swift

Question

Updating cartArray from ViewModel doesn't append to the current elements, but adds object everytime freshly. I need to maintain cartArray as global array so that it can be accessed from any view of the project. I'm adding elements to cartArray from ViewModel. I took a separate class DataStorage which has objects that can be accessible through out the project
Example_AppApp.swift
import SwiftUI
#main
struct Example_AppApp: App {
var body: some Scene {
WindowGroup {
ContentView().environmentObject(DataStorage())
}
}
}
DataStorage.swift
import Foundation
class DataStorage: ObservableObject {
#Published var cartArray = [Book]()
}
ContentView.swift
import SwiftUI
struct ContentView: View {
#State var showSheetView = false
var body: some View {
NavigationView{
ListViewDisplay()
.navigationBarItems(trailing:
Button(action: {
self.showSheetView.toggle()
}) {
Image(systemName: "cart.circle.fill")
.font(Font.system(.title))
}
)
}.sheet(isPresented: $showSheetView) {
View3()
}
}
}
struct ListViewDisplay: View{
var book = [
Book(bookId: 1 ,bookName: "Catch-22"),
Book(bookId: 2 ,bookName: "Just-Shocking" ),
Book(bookId: 3 ,bookName: "Stephen King" ),
Book(bookId: 4,bookName: "A Gentleman in Moscow"),
]
var body: some View {
List(book, id: \.id) { book in
Text(book.bookName)
NavigationLink(destination: View1(book: book)) {
}
}
}
}
View1Modal.swift
import Foundation
struct Book: Codable, Identifiable {
var id:String{bookName}
var bookId : Int
var bookName: String
}
struct BookOption: Codable{
var name: String
var price: Int
}
View1ViewModel.swift
import Foundation
import Combine
class View1ViewModel : ObservableObject{
var dataStorage = DataStorage()
func addBook (bookId:Int ,bookName : String){
dataStorage.cartArray.append(Book(bookId:bookId, bookName: bookName)) // Adding to global array
print(dataStorage.cartArray)
}
}
View1.swift
import SwiftUI
struct View1: View {
#ObservedObject var vwModel = View1ViewModel()
#EnvironmentObject var datastrg: DataStorage
var book:Book
var body: some View {
Text(book.bookName).font(.title)
Spacer()
Button(action: {
vwModel.addBook(bookId: book.bookId, bookName: book.bookName)
}, label: {
Text("Add Book to Cart")
.frame(maxWidth: .infinity, minHeight: 60)
.background(Color.red)
.foregroundColor(Color.white)
.font(.custom("OpenSans-Bold", size: 24))
})
}
}
View3.swift
import SwiftUI
struct View3: View {
#EnvironmentObject var datastorage : DataStorage
var body: some View {
NavigationView {
List(datastorage.cartArray,id:\.id){book in
VStack{
Text(book.bookName)
.font(.custom("OpenSans-Bold", size: 20))
}
}
.navigationBarTitle(Text("Cart"), displayMode: .inline)
}
}
}
When addBook func is called for the first time it prints as
[Example_App.Book(bookId: 1, bookName: "Catch-22")]
When I go back and come back to this View1 and add another book by calling addBook func it adds as new object to cartArray
[Example_App.Book(bookId: 3, bookName: "Stephen King")]
Printing number of elements in cartArray gives as 1 element instead of 2 elements. When I go to View3 and display the Books in list, cartArray shows as empty(0 elements)
I think there is something wrong with var dataStorage = DataStorage() in ViewModel class. Everytime this is being created freshly, so the prevoius values are not stored. But I couldn't understand how to preserve its state
How to display List in View3 ? Any ideas/ suggestions will be helpful

Answer 1

You need to have one instance of DataStorage that gets passed around. Any time you write DataStorage() that creates a new instance.
.environmentObject will let you inject that one instance into the view hierarchy. Then, you can use the #EnvironmentObject property wrapper to access it within a View.
Inside View1, I used onAppear to set the dataStorage property on View1ViewModel -- that means that it has to be an optional on View1ViewModel since it will not be set in init. The reason I'm avoiding setting it in init is because an #EnvironmentObject is not set as of the init of the View -- it gets injected at render time.
#main
struct Example_AppApp: App {
var dataStorage = DataStorage()
var body: some Scene {
WindowGroup {
ContentView().environmentObject(dataStorage)
}
}
}
class DataStorage: ObservableObject {
#Published var cartArray = [Book]()
}
struct ContentView: View {
#State var showSheetView = false
var body: some View {
NavigationView{
ListViewDisplay()
.navigationBarItems(trailing:
Button(action: {
self.showSheetView.toggle()
}) {
Image(systemName: "cart.circle.fill")
.font(Font.system(.title))
}
)
}.sheet(isPresented: $showSheetView) {
View3()
}
}
}
struct ListViewDisplay: View {
var book = [
Book(bookId: 1 ,bookName: "Catch-22"),
Book(bookId: 2 ,bookName: "Just-Shocking" ),
Book(bookId: 3 ,bookName: "Stephen King" ),
Book(bookId: 4,bookName: "A Gentleman in Moscow"),
]
var body: some View {
List(book, id: \.id) { book in
Text(book.bookName)
NavigationLink(destination: View1(book: book)) {
}
}
}
}
struct Book: Codable, Identifiable {
var id:String{bookName}
var bookId : Int
var bookName: String
}
struct BookOption: Codable{
var name: String
var price: Int
}
class View1ViewModel : ObservableObject{
var dataStorage : DataStorage?
func addBook (bookId:Int ,bookName : String) {
guard let dataStorage = dataStorage else {
fatalError("DataStorage not set")
}
dataStorage.cartArray.append(Book(bookId:bookId, bookName: bookName)) // Adding to global array
print(dataStorage.cartArray)
}
}
struct View1: View {
#ObservedObject var vwModel = View1ViewModel()
#EnvironmentObject var datastrg: DataStorage
var book:Book
var body: some View {
Text(book.bookName).font(.title)
Spacer()
Button(action: {
vwModel.addBook(bookId: book.bookId, bookName: book.bookName)
}, label: {
Text("Add Book to Cart")
.frame(maxWidth: .infinity, minHeight: 60)
.background(Color.red)
.foregroundColor(Color.white)
.font(.custom("OpenSans-Bold", size: 24))
})
.onAppear {
vwModel.dataStorage = datastrg
}
}
}
struct View3: View {
#EnvironmentObject var datastorage : DataStorage
var body: some View {
NavigationView {
List(datastorage.cartArray,id:\.id){book in
VStack{
Text(book.bookName)
.font(.custom("OpenSans-Bold", size: 20))
}
}
.navigationBarTitle(Text("Cart"), displayMode: .inline)
}
}
}

Answer 2

You are not calling your function addBook anywhere, add an onappear to your view3 calling the function and your list will populate with data.