Create a DetailViewModel within a ParentView's body and then pass it to the DetailView

Question

Let me preface this by saying that this is not a problem. This is a solution I stumbled upon that works really well. I need clarification as to why this works and whether this is a feature because I haven't found a lot of info that describes this. I have a large app that employs this throughout so I need to make sure this solution will stick around in the long term.

I needed a way to pass in many parameters to a new unique View, and to use those parameters to create a network request that was called only once. An example would be a ProductsView which consists of a List of products. When an individual product is tapped within the List a NavigationLink segues to a ProductView. The parameters are passed to create a network request within the ProductViewModel which is then used to update the ProductView.

Some things I tried include...

Creating a @StateObject var productViewModel = ProductViewModel within ProductsView. That didn't work because each ProductView is unique and needs it's own ProductViewModel.

Using @Binding vars within ProductView and then passing them into ProductViewModel within .onAppear to make a network request. That didn't work because the @Binding vars didn't work with nested views within ProductView.

Using regular vars such as var productID: Int or @State var productID: Int. This worked but proved to be way too messy and the network request being called within .onAppear was unreliable being called multiple times in some cases.

https://stackoverflow.com/a/62636048/6724254 way to hacky for me.

The solution I found that works the best is to create ProductViewModels ProductView(productViewModel: ProductViewModel(productID: product.productID))) within the NavigationLink destination call. A very simple example...

import SwiftUI

struct Product: Identifiable{
    var id = UUID()
    var productID = 0
    var name = ""
}

class ProductViewModel: ObservableObject {
    
    @Published var product = Product()
    
    init(productID: Int){
        
        print("init ProductViewModel ProductID: \(productID)")
        
        getFromNetwork(productID: productID)
    }
    
    func getFromNetwork(productID: Int){
        
        // network request made here
        DispatchQueue.main.asyncAfter(deadline: .now() + 0.5) {
            
            self.product = Product(productID: productID, name: "Product Name \(productID)")
            
        }
        
    }
   
}

// Each ProductView must be unique
struct ProductView: View {
    
    @StateObject var productViewModel: ProductViewModel
    
    var body: some View {
        if productViewModel.product.productID > 0{
            VStack{

                Text("Current Product: " + productViewModel.product.name)
                
                NavigationLink(destination: ProductView(productViewModel: ProductViewModel(productID: Int.random(in: 1..<100)))) {
                    Text("Recommended Product")
                }
            }
        }
    }
    
}

struct ProductsView: View {
    
    @State var products = [Product(productID: 1), Product(productID: 2), Product(productID: 3), Product(productID: 4), Product(productID: 5), Product(productID: 6)]
    
    var body: some View {
        NavigationView {
            
            List(products) { product in
                NavigationLink(destination: ProductView(productViewModel: ProductViewModel(productID: product.productID))) {
                    Text("Product ID: \(product.productID)")
                }
            }
            .navigationTitle("Products")
        }
        
    }
}

So my question is whether this solution is reliable in ways that I haven't foreseen, and will it stick around in the long term?

Answer 1

In any case, if it helps – this would be the classic way to load all products into an array, and pass that down:

struct Product: Identifiable{
    var id = UUID()
    var productID = 0
    var name = ""
}

class ProductViewModel: ObservableObject {
    
    @Published var products: [Product]
    
    init(){
        products = []
        for productID in 1...20 {
            getFromNetwork(productID: productID)
        }
    }
    
    func getFromNetwork(productID: Int){
        // network request made here
        DispatchQueue.main.asyncAfter(deadline: .now() + 0.5) {
            let new = Product(productID: productID, name: "Product Name \(productID)")
            self.products.append(new)
        }
    }
}

// Each ProductView must be unique
struct ProductView: View {
    
    var product: Product
    
    @EnvironmentObject var model: ProductViewModel
    
    var body: some View {
        if product.productID > 0 {
            VStack{
                
                Text("Current Product: " + product.name)
                
                NavigationLink(destination: ProductView(product: model.products[Int.random(in: 0..<20)])) {
                    Text("Recommended Product")
                }
            }
        }
    }
    
}

struct ProductsView: View {
    
    @StateObject var model = ProductViewModel()
    
    var body: some View {
        NavigationView {
            
            List(model.products) { product in
                NavigationLink(destination: ProductView(product: product)) {
                    Text("Product ID: \(product.productID)")
                }
            }
            .navigationTitle("Products")
        }
        .environmentObject(model)
    }
}