I have almost completed the challenge on day 59, but I am trying to figure out part 3 of the challenge where we are supposed to allow our own view FilteredList to accept an array of SortDescriptor.

Apparently [SortDescriptor] is not a valid type. Obviously I am not understanding something, but I can not figure out what I am missing. Can anybody give me a pointer on how to proceed?

FilteredList

import CoreData
import SwiftUI

struct FilteredList<T: NSManagedObject, Content: View>: View {

    @FetchRequest var fetchRequest: FetchedResults<T>
    let content: (T) -> Content

    var body: some View {
        List(fetchRequest, id: \.self) { item in
            self.content(item)
        }
    }

    init(filterKey: String, filterValue: String, predicate: MyPredicate, sortDescriptors: [SortDescriptor], @ViewBuilder content: @escaping (T) -> Content) {
        var stringPredicate: String

        switch predicate {
        case .beginsWith:
            stringPredicate = "BEGINSWITH"
        case .contains:
            stringPredicate = "CONTAINS"
        case .predIN:
            stringPredicate = "IN"
        }

        _fetchRequest = FetchRequest<T>(sortDescriptors: sortDescriptors, predicate: NSPredicate(format: "%K \(stringPredicate) %@", filterKey, filterValue))
        self.content = content
    }
}
enum MyPredicate {
    case beginsWith, contains, predIN
}

ContentView

import CoreData
import SwiftUI

struct ContentView: View {
    @Environment(\.managedObjectContext) var moc
    @State private var lastNameFilter = "A"

    var body: some View {
        VStack {
            // list of matching singers
            FilteredList(filterKey: "lastName",
                         filterValue: lastNameFilter,
                         predicate: .beginsWith,
                         sortDescriptors: [
                            SortDescriptor(\.wrappedLastName),
                            SortDescriptor(\.wrappedFirstName, order: .reverse)
                         ]) { (singer: Singer) in
                Text("\(singer.wrappedFirstName) \(singer.wrappedLastName)")
            }
        }
    }
}

Hi,

thanks for your input, I think it gave me a better understanding regarding the typing. I went and put the following line in my ContentView:

@State private var singerSortDescriptors: [SortDescriptor<Singer>] = [SortDescriptor(\.wrappedLastName),
                                                                       SortDescriptor(\.wrappedFirstName, order: .reverse)]

This state variable was then used in the FilteredList(...).

I also changed the initializer of FilteredList :

init(filterKey: String,
      filterValue: String,
      predicate: MyPredicate,
      sortDescriptors: [SortDescriptor<T>],
      @ViewBuilder content: @escaping (T) -> Content) {...}

unfortunately I get the following error at runtime:

Thread 1: Fatal error: Singer must be introspectable by the objective-c runtime in order to use it as the base type of a `SortDescriptor`.

thanks

you are using wrong paths:

[SortDescriptor(\.wrappedLastName),
  SortDescriptor(\.wrappedFirstName, order: .reverse)]

those are used to display strings on views, on CoreData properties we changed it to this, right?

    var wrappedFirstName: String {
        firstName ?? "Unknown"
    }

    var wrappedLastName: String {
        lastName ?? "Unknown"
    }

But to access items in CoreData Entity we need to use real paths so you need to use it as follows:

[SortDescriptor(\.lastName),
  SortDescriptor(\.firstName, order: .reverse)]

yes, you are absolutley right. I think i got it now. I changed the properties as you suggested and the problem went away.

Thank you so much for your help.

Nice! Glad it helped :)