Passing item using ForEach into DetailView through NavigationLink-CodePudding

I'm trying to clean up my code a bit by creating another file/view called DetailView that will display all the actual values for each item when the user clicks on them from the 'ForEach' code. However, its giving me an error of: Missing argument for parameter 'item' in call and its throwing it on the DetailViews_Previews. Why and how do I fix this? Thanks.

LISTVIEW

struct ListView: View {
   @Environment(\.managedObjectContext) private var viewContext
   @FetchRequest(sortDescriptors: [NSSortDescriptor(keyPath:\Item.todaysDate, ascending: false)],animation: .default) 
   private var items: FetchedResults<Item>

var body: some View {
NavigationView {
     List {
        ForEach(items) { item in
            NavigationLink {
                 DetailView(item:item).environment(\.managedObjectContext, self.viewContext)
            } label: {
                 VStack {
                     Text("\(item.hoursSlept, specifier: "%.2f") hrs")
                         .bold()
                         .font(.system(size:18))
                         .padding(.trailing, 50)
                 }
            }
}}}}}

DETAILVIEW

struct DetailView: View {
    
    @Environment(\.managedObjectContext) private var viewContext
    @ObservedObject var item: Item

var body: some View {
    VStack {
       if item.headacheToggle == true {
            Image(systemName: "checkmark.circle").imageScale(.large)
                  .foregroundStyle(.red)
                  .font(.system(size:15))
       }
       else {
           Image(systemName: "x.circle").imageScale(.large)
                 .foregroundStyle(.green)
                 .font(.system(size:15))
       }
    }
}}

struct DetailView_Previews: PreviewProvider {
    static var previews: some View {
        DetailView().environment(\.managedObjectContext, ListViewModel.preview.container.viewContext)
    }
}

CodePudding user response：

You need to fetch an item from the preview context, here is one way:

struct DetailView_Previews: PreviewProvider {
    
    static var firstItem: Item? {
        let context = PersistenceController.preview.container.viewContext
        let fetchRequest = Item.fetchRequest()
        fetchRequest.fetchLimit = 1
        let results = try? context.fetch(fetchRequest)
        return results?.first
    }
    
    static var previews: some View {
        if let item = firstItem {
            DetailView(item: item)
        }
        else {
            Text("Item not found")
        }
    }
}