Type of expression is ambiguous without more conte

问题:

I'm trying to refer to an [Item] list within an @EnvironmentObject however when accessing it within a SwiftUI List, I get the error. What I don't understand is, this error doesn't pop up when following Apple's Landmark tutorial.

As far as I can tell, the [Item] list is loading correctly as I can print it out and do other functions with it. It just bugs out when using it for a SwiftUI List Is there something I've missed?

ItemHome.swift:

struct ItemHome : View {

    @EnvironmentObject var dataBank: DataBank

    var body: some View {
        List {
            ForEach(dataBank.itemList) { item in
                Text("\(item.name)") // Type of expression is ambiguous without more context
            }
        }
    }
}

Supporting code below:

Item Struct:

struct Item {

    var id: Int
    var uid: String
    var company: String
    var item_class: String
    var name: String
    var stock: Int
    var average_cost: Decimal
    var otc_price: Decimal
    var dealer_price: Decimal
    var ctc_price: Decimal
}

DataBank.swift:

final class DataBank : BindableObject {
    let didChange = PassthroughSubject<DataBank, Never>()

    var itemList: [Item] = load("itemsResults.json") {
        didSet {
            didChange.send(self)
        }
    }
}

func load<T: Decodable>(_ filename: String, as type: T.Type = T.self) -> T {
let data: Data

guard let file = Bundle.main.url(forResource: filename, withExtension: nil)
    else {
        fatalError("Couldn't find \(filename) in main bundle.")
}

do {
    data = try Data(contentsOf: file)
} catch {
    fatalError("Couldn't load \(filename) from main bundle:\n\(error)")
}

do {
    let decoder = JSONDecoder()
    return try decoder.decode(T.self, from: data)
} catch {
    fatalError("Couldn't parse \(filename) as \(T.self):\n\(error)")
}

}

itemsResults.json:

[
    {
        "id": 1,
        "uid": "a019bf6c-44a2-11e9-9121-4ccc6afe39a1",
        "company": "Bioseed",
        "item_class": "Seeds",
        "name": "9909",
        "stock": 0,
        "average_cost": 0.0,
        "otc_price": 0.0,
        "dealer_price": 0.0,
        "ctc_price": 0.0
    },
    {
        "id": 2,
        "uid": "a019bf71-44a2-11e9-9121-4ccc6afe39a1",
        "company": "Pioneer",
        "item_class": "Seeds",
        "name": "4124YR",
        "stock": 0,
        "average_cost": 0.0,
        "otc_price": 0.0,
        "dealer_price": 0.0,
        "ctc_price": 0.0
    }
]

回答1:

Apparently I missed making sure my models (Item in this case) conformed to the Identifiable protocol fixed it. Still, I wish Apple was more clear with their error messages.

回答2:

As you mentioned in your answer, a ForEach needs a list of Identifiable objects. If you don't want to make your object implement that protocol (or can't for some reason), however, here's a trick:

item.identifiedBy(\.self)

回答3:

To conform to Identifiable, just give the id or uid variable a unique value.

An easy way to do this is this:

var uid = UUID()

So your full struct would be:

struct Item: Identifiable {

    var id: Int
    var uid = UUID()
    var company: String
    var item_class: String
    var name: String
    var stock: Int
    var average_cost: Decimal
    var otc_price: Decimal
    var dealer_price: Decimal
    var ctc_price: Decimal
}

回答4:

I had the same problem and it wasn't something related to the line itself, it was related to the curly braces/brackets, so that if someone faced the same problem and doesn't know where the problem is, try to trace the curly braces and the brackets