SwiftUI: Use generic type for List - Stack Overflow

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I want to have a SwiftUI List to be filled with array items that is a part protocol type. Here is a snippet I have :

import Foundation
import SwiftUI

struct ScanItem: Hashable, Equatable, Identifiable {
    let id: UUID
    let name: String
    let rssi: Int
    let peripheral: Peripheral?
    
    func hash(into hasher: inout Hasher) {
        hasherbine(id)
    }
    
    static func == (lhs: ScanItem, rhs: ScanItem) -> Bool {
        return lhs.id == rhs.id
    }
}

protocol ScanProtocol: ObservableObject {
    var isScanning: Bool { get }
    var peripherals: [ScanItem] { get }
    var error: String? { get }

    func startScan()
    func stopScan()
}


struct FoundDeviceListView<Model>: View where Model: ScanProtocol {
    @ObservedObject var scanModel: Model
    
    var body : some View {
        List(scanModel.peripherals) { item in
            Text("\(item.name) ( \(item.identifier) ) \(item.rssi) dBm")
        }
    }
}

#Preview {
    @Previewable @StateObject var model = ScanEmulator()
    FoundDeviceListView(scanModel: model)
}

But I get 2 compile-time issues:

1. Cannot convert value of type '[ScanItem]' to expected argument type 'Binding'
2. Generic parameter 'Data' could not be inferred

What should be done to fix it?

I want to have a SwiftUI List to be filled with array items that is a part protocol type. Here is a snippet I have :

import Foundation
import SwiftUI

struct ScanItem: Hashable, Equatable, Identifiable {
    let id: UUID
    let name: String
    let rssi: Int
    let peripheral: Peripheral?
    
    func hash(into hasher: inout Hasher) {
        hasherbine(id)
    }
    
    static func == (lhs: ScanItem, rhs: ScanItem) -> Bool {
        return lhs.id == rhs.id
    }
}

protocol ScanProtocol: ObservableObject {
    var isScanning: Bool { get }
    var peripherals: [ScanItem] { get }
    var error: String? { get }

    func startScan()
    func stopScan()
}


struct FoundDeviceListView<Model>: View where Model: ScanProtocol {
    @ObservedObject var scanModel: Model
    
    var body : some View {
        List(scanModel.peripherals) { item in
            Text("\(item.name) ( \(item.identifier) ) \(item.rssi) dBm")
        }
    }
}

#Preview {
    @Previewable @StateObject var model = ScanEmulator()
    FoundDeviceListView(scanModel: model)
}

But I get 2 compile-time issues:

1. Cannot convert value of type '[ScanItem]' to expected argument type 'Binding'
2. Generic parameter 'Data' could not be inferred

What should be done to fix it?

• list
• generics
• swiftui

Share Improve this question Follow edited 2 days ago malhal 30.9k77 gold badges123123 silver badges150150 bronze badges asked 2 days ago DmitryDmitry 2,16833 gold badges2323 silver badges3434 bronze badges 3

• Where is the property identifier defined? I'm able to compile your code after removing item.identifier – SwiftyJoeyy Commented 2 days ago
• Dont override Hashable and Equatable to use just the id – lorem ipsum Commented 2 days ago
• @SwiftyJoeyy upsie, I renamed 'identifier' to 'id' but fot about it while making a valid code snippet. I had a deeper look into the c-tor of NavigationLink and found out that it is possible to use 'value' argument to 'export' a custom type to be used with . navigationDestination modifier – Dmitry Commented 2 days ago

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2 Answers 2

Sorted by: Reset to default 0

// Generic View with List
struct FoundDeviceListView<ViewModel, Data>: View where ViewModel: ScanViewModelProtocol, Data: RandomAccessCollection, Data.Element: Identifiable {
    @ObservedObject var scanModel: ViewModel
    var items: Data

    var body: some View {
        List(items) { item in
            if let device = item as? ScanViewListItem {
                Text("\(device.name) (\(device.id)) \(device.rssi) dBm")
            }
        }
    }
}

FoundDeviceListView(scanModel: ScanViewModelEmulator(), items: 
ScanViewModelEmulator().peripherals)

I guess, I found a solution - hope that would safe some time for future readers

struct FoundDeviceListView<Model>: View where Model: ScanProtocol {
    @ObservedObject var scanModel: Model
    
    var body : some View {
        List(scanModel.peripherals, id: \.identifier) { peripheral in
            NavigationLink(
                "\(peripheral.name) ( \(peripheral.identifier) ) \(peripheral.rssi) dBm",
                value: peripheral
            )
            .frame(height: 100, alignment: .center)
            .font(scanModel.isScanning ? .title : .largeTitle.bold())
            .foregroundStyle(.blue)
        }
        .navigationDestination(for: ScanItem.self) { item in
            ConnectedDeviceView(uuid: item.identifier, deviceName: item.name)
        }
        .navigationTitle("Обнаруженные устройства")
        .font(.title)
        .disabled(scanModel.isScanning)
    }
}

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