我该如何解决：由于“未知上下文”而无法投放？

如何解决我该如何解决：由于“未知上下文”而无法投放？

场景：
函数需要一个通用参数（ CovidResource ）来从服务器获取数据，该服务器将根据函数参数 CovidResource 的值以特定格式返回数据。>

目的是使用一（1）个功能以格式/端点的形式从各种端点中获取数据。

该函数以 CovidResource 格式返回结构 AppleSubRegions （在本示例中为通过通用值的任何可能的数据类型之一）。

 let url = URL(string: "https://disease.sh/v3/covid-19/apple/countries/CANADA")!
        countryListViewModel.getList(urlDataModel: CovidResource<AppleSubRegions>(url: url))

struct AppleSubRegions: Codable {
    let country,subregion: String
    let data: [AppleDatum]
}

import Combine
import UIKit

protocol URLResource {
    associatedtype DataModel: Decodable
    var url: URL? { get }
}

struct CovidResource<T: Decodable>: URLResource {
    typealias DataModel = T
    var url = URL(string: "https://disease.sh/v3/covid-19/apple/countries/Canada")
}

// =====================================================================================================

class CountryRegionListModel: ObservableObject {
    @Published var countryRegionList: [String] = []

    // Data Persistence:
    var cancellables: Set<AnyCancellable> = []

    // ---------------------------------------------------------------------------

    func getList<Resource>(urlDataModel: Resource) where Resource: URLResource {
        let remoteDataPublisher = URLSession.shared.dataTaskPublisher(for: urlDataModel.url!)
            .map(\.data)
            .handleEvents(receiveOutput: { data in
                print(String(data: data,encoding: .utf8)!)
              })
            .receive(on: DispatchQueue.main)
            .decode(type: Resource.DataModel.self,decoder: JSONDecoder())
        
            //.print("getList: ")
        
        remoteDataPublisher
            .eraseToAnyPublisher()
            .sink(receiveCompletion: { completion in
                switch completion {
                case .finished:
                    print("Publisher Finished")
                case let .failure(anError):
                    Swift.print("\nReceived error: ",anError)
                }
            },receiveValue: { someValue in
                print("\n\n ---- Model: \(someValue)")
                DataSource.shared.countryName = (someValue as! AppleSubRegions).country
               
            }).store(in: &cancellables)
    }
}

您可以看到返回的数据类型为“ AppleSubRegions ”：
（注意'未知上下文 ...）吗？

(lldb) po type(of: someValue)
Covid19.TabNavView.(unknown context at $10bb96490).(unknown context at $10bb96504).AppleSubRegions

我可以通过调试器看到国家/地区“ 加拿大”：

---- Model: AppleSubRegions(country: "Canada",subregions: ["Alberta","Calgary","Edmonton","British Columbia","Vancouver","Manitoba","New Brunswick","Newfoundland and Labrador","Northwest Territories","Halifax","Nova Scotia","Ontario","Ottawa","Toronto","Prince Edward Island","Montreal","Quebec","Saskatchewan","All","Yukon Territory"])
(lldb) po someValue.country
"Canada"

我尝试通过代码重复调试器的操作：

...但是您可以看到，数据模型不知道'国家'：

但是我无法访问其成员。

所以我尝试将'someValue'强制转换为 AppleSubRegions 类型：

哪个崩溃了编译。

问题：如何将 CovidResource 转换为 AppleSubRegions 正确的（Swift数据项）？

---

建议尝试
1.通过

...receiveValue { someValue: AppleSubRegions in

但是我遇到了编译器语法错误：

1. 添加其他约束：
   

但这会导致另一个编译器错误：

解决方法

如果您将类型进一步限制为AppleSubRegions，这应该可以工作：

func getList<R: URLResource>(urlDataModel: R) where R.DataModel == AppleSubRegions {
    let remoteDataPublisher = Just(json)
            .receive(on: DispatchQueue.main)
            .decode(type: R.DataModel.self,decoder: JSONDecoder())

    remoteDataPublisher
        .sink(
            receiveCompletion: {...},receiveValue: { someValue in
               print(someValue.country)
            }).store(in: &c)
}