Question 108524 in IOS Swift Question posted in
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Ios swift – Why can't I access the id across views?

In my project, the user can have two favourite products. They can change them by tapping on one(ProductView). After tapping one, a view called ‘ProductSheet’ is displayed. I try to carry the id from the previous view but it is not there. I need to carry the id across to ‘ProductSheet’ and ‘ProductRowView’ in order to carry out the function of changing the favourite product.

I don’t understand why product_id has no value in the ‘ProductSheet’ & ‘ProductRowView’ views. Here is a shortened simplified version of the code:

struct FavouriteProducts: View {
    
    @StateObject var favouriteProductsModel = FavouriteProductsViewModel()
    @State private var showingSheet = false
    @State var selectedProduct: String?
    @State var product_id: String?
        
    
    var body: some View {
        
        ZStack {
            let defaults = UserDefaults.standard
            let keyString: String? = defaults.string(forKey: "key") ?? ""
            
            VStack {
                
                HStack {
                    
                    Text("Tap to change favourite product")
                }
                
                HStack(spacing: 25) {
                    
                    ForEach(favouriteProductsModel.favourite_products, id: .id){ product in
                        
                        VStack {
                                                                                                                
                            Image("ProductImage")
                                .resizable()
                                                    
                            Text(String(product.product_name ?? ""))

                        }
                        .onTapGesture {
                            selectedProduct = product.id
                            self.product_id = product.id ?? ""
                            self.showingSheet = true
//selectedProduct does have a value in this print statement
                            print("Tapped Product ID: (String(describing: selectedProduct))")
                        }
                        .sheet(item: $selectedProduct) {
                            favouriteProductsModel.fetchFavouriteProducts(key: keyString ?? "")
                        } content: { item in
                            ProductSheet(product_id: selectedProduct ?? "")
                        }
                    }
                }
            }
        }
        .onLoad {
            let defaults = UserDefaults.standard
            let keyString: String? = defaults.string(forKey: "key") ?? ""
            self.favouriteProductsModel.fetchFavouriteProducts(key: keyString ?? "")
        }
    }
}

struct ProductSheet: View {
    
    @StateObject var marketplaceModel = MarketplaceViewModel()
    @State var product_id: String?

    var body: some View {


        VStack {
            
            // The product_id here is not being displayed, because the variable has no value
            Text(product_id ?? "")
            
            ForEach(marketplaceModel.filteredProduct, id:.self){ product in
                
                ProductRowView(productData: product, product_id: product_id ?? "")
            }
                        
        }
    }
}

struct ProductRowView: View {
    
    @Environment(.dismiss) var dismiss
    @StateObject var favouriteProductsModel = FavouriteProductsViewModel()
    @State private var isShowingDetailView = false
    @State var selectedProduct : ProductTile?
    @State var new_id = ""
    var productData: ProductRow
    var product_id: String
    
    var body: some View {
        
        VStack {
            
            HStack {
                Text(productData.title)
                
                HStack {
                    NavigationLink("", isActive: $isShowingDetailView) {
                        ProductSeeAllView(productData: productData, product_id: productData.id)
                    }.navigationTitle("")
                    
                    Button("See All") {
                        isShowingDetailView = true
                    }
                    Image(systemName: "chevron.right")
                }
            }
            
            HStack {
                ScrollView {
                    HStack {
                        ForEach(productData.products ?? []) { product in
                            ProductView(productData: product)
                                .onTapGesture {
                                    new_id = product.id ?? ""
                                    selectedProduct = product
                                    print("Product id: (selectedProduct?.id ?? "")")
                                    let defaults = UserDefaults.standard
                                    let keyString: String? = defaults.string(forKey: "key") ?? ""
                                    
                                    favouriteProductsModel.changeFavouriteProducts(key: keyString ?? "", current_id: product_id, new_id: new_id ) { (success) in
                                        if success {
                                            dismiss()
                                        } else {
                                            print("Unsuccessful...")
                                        }
                                    }
                                }
                        }
                    }
                }
            }
        }
    }
}

When initialising ‘ProductSheet’ & ‘ProductRowView’ I should be passing the product_id through but it doesn’t work. Why is this happening?

EDIT:
With further testing, it seems that the id is passed through if the sheet is initialised for a second time. It never seems to work first time though.

Tags:

3

Answers


  1. Chosen as BEST ANSWER
    0

    The issue was, the data was not being passed through to the sheet the first time it was initialised. The following code stopped that bug:

    @State private var showingSheet = false

        .sheet(isPresented: Binding(
                                        get: { showingSheet },
                                        set: { showingSheet = $0 }
                                    )) {
                                        ProductSheet(product_id: selectedProduct ?? "")
                                    }

  2. 0

    I simplified your code to show you a working solution.

    The sheet is created at the init of the view so the ProductSheet is initialized with a nil product. You have to add @Binding to obtain the desired behavior.

    struct Product: Identifiable {
    var id: Int
    var name: String
}

let products = [
    Product(id: 1, name: "Product 1"),
    Product(id: 2, name: "Product 2")
]

struct FavouriteProducts: View {
    @State private var showingSheet = false
    @State private var selectedProduct: Product?

    var body: some View {
        VStack {
            Text("Tap to change favourite product")

            ForEach(products){ product in
                Text(product.name)
                    .onTapGesture {
                        selectedProduct = product
                        showingSheet = true
                    }
            }
        }
        .sheet(isPresented: $showingSheet) {
            ProductSheet(product: $selectedProduct)
        }
    }
}

struct ProductSheet: View {
    @Binding var product: Product?

    var body: some View {
        Text(product?.name ?? "?")
    }
}
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  3. 0

    It should be let instead of @State var. With a let, body will be called automatically then the value passed in changed from the last time this View struct was init, e.g.

    struct ProductSheet: View {

    // Bad code! don't misuse StateObject for view model objects just use the View structs.
    //@StateObject var marketplaceModel = MarketplaceViewModel()

    let productID: String

    Fyi we don’t need view model objects in SwiftUI because that is the job of the View struct. @StateObject is for when you need to store a reference type in an @State, e.g. when doing something async. If you use @StateObject to try to implement view models you’ll run into the kind of consistency bugs SwiftUI’s design of immutable View structs for view data was designed to eliminate.

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