SwiftUI Update Model with Button and Increase amount - swiftui

Question

i want to increase a product of its tapped count. so if the user press a button the Model needs to be updated and the amount += 1
I try the following code and the model does not update the amount.
struct GridCell: View {
#EnvironmentObject var order: Order
class ViewModel: ObservableObject {
let objectWillChange = PassthroughSubject<Void, Never>()
#Published var product : Product {
willSet {
self.objectWillChange.send()
}
}
init(product: Product) {
self.product = product
}
public func increaseAmount() {
self.product.amount += 1
self.objectWillChange.send()
print("\(self.product.amount) / \(self.product.id)")
}
}
func updatePos(){
self.viewModel.increaseAmount()
let itempreis = viewModel.product.preis
order.totalAmount += itempreis
print(order.totalAmount)
}
#ObservedObject var viewModel: ViewModel
var body: some View {
Button(action: {
print("TAPPED")
self.updatePos()
}) {
...
}
}
and GridCell would be
GridCell(viewModel: GridCell.ViewModel(product: $0))
and Product is
struct Product : Identifiable, Equatable, Decodable {
var id: String
var name: String
let preis: Double
var amount: Int
}
In my print statement the amount is not updating and every time I press the button the value is like 1.
What did I forget?

Answer 1

Try this
public func increaseCharacterStrength() {
self.product.amount += 1
}
Because Product is a struct when you were creating the variable var viewproduct = self.product you were creating a local copy of product, so viewproduct.amount += 1 just increases the amount for that local variable, not for the actual model.

Answer 2

I think you are not defining view model correctly. Since I do not have the structure of the product and order, I simplified the model to meet the needs of our discussion. For the example provided below, you can create the instance of GridCell (like GridCell()) and tapping the button increases the quantity by 1. Also note one can simplify further by using #Published property wrapper in the view model instead of Passthrough
class Order: ObservableObject {
#Published var totalAmount : Int = 0
}
struct Product {
var id = UUID()
var amount: Int = 0
var preis: Int = 0
}
struct GridCell: View {
#EnvironmentObject var order: Order
func updatePos() {
self.viewModel.increaseCharacterStrength()
let itempreis = self.viewModel.product.preis
order.totalAmount += itempreis
//print(order.totalAmount)
print("---- \(self.viewModel.product.amount) / \(self.viewModel.product.id)")
}
#ObservedObject var viewModel = ViewModel(product: Product())
var body: some View {
Button(action: {
print("TAPPED")
self.updatePos()
}) {
Text("Increase order")
}
}
}
class ViewModel: ObservableObject {
let objectWillChange = PassthroughSubject < Void,
Never > ()
var product: Product {
willSet {
self.objectWillChange.send()
}
}
init(product: Product) {
self.product = product
}
public func increaseCharacterStrength() {
self.product.amount += 1
self.objectWillChange.send()
}
}