快速组合：已完成，但出现错误 [-999] 错误域=NSURLError域代码=-999 "cancelled"

Question

我试图通过restful API获取数据，但存在问题。当我尝试获取数据时，错误立即出现:

20121-08-24 17:36:44.851463+0200国家[1498:19786]任务<3FF6E673-52AD-47FE-9342-229E2CE99859>.<1>完成错误[-999]错误域=NSURLErrorDomain代码=-999 "cancelled"用户信息= {NSErrorFailingURLStringKey = https://restcountries。eu/rest/v2/all, NSLocalizedDescription=cancelled, NSErrorFailingURLKey=https://restcountries.eu/rest/v2/all}

每次都显示。知道怎么解决吗?

APIService:

final class APIService: APIServiceProtocol {

func fetchAllCountries(url: URL) -> AnyPublisher<[Country], APIError> {

let request = URLRequest(url: url)

return URLSession.DataTaskPublisher.init(request: request, session: .shared)
.tryMap { data, response in
guard let httpResponse = response as? HTTPURLResponse, 200..<300 ~= httpResponse.statusCode else {
throw APIError.unknown
}

return data
}
.decode(type: [Country].self, decoder: JSONDecoder())
.mapError { error in
if let error = error as? APIError {
return error
} else {
return APIError.apiError(reason: error.localizedDescription)
}
}
.eraseToAnyPublisher()
}
}

ListViewModel:

import SwiftUI
import Combine
class ListViewModel: ObservableObject {

private let apiService: APIServiceProtocol
@Published var countries = [Country]()

init(apiService: APIServiceProtocol = APIService()) {
self.apiService = apiService
}

func fetchCountries() {

guard let url = URL(string: "https://restcountries.eu/rest/v2/all") else { return }

let publisher = apiService.fetchAllCountries(url: url)
.receive(on: DispatchQueue.main)
.sink(receiveCompletion: { completion in
switch completion {
case .finished:
break
case .failure(let error):
print(error.localizedDescription)
}
}, receiveValue: { data in
self.countries = data
print(data)
})
publisher.cancel()
}

}

Answer 1

你必须给发行商分配一个strong引用，否则它会立即取消自身。

创建属性

var cancellable : AnyCancellable?

分配

cancellable = apiService.fetchAllCountries(url: url) ...

并取消finished范围内的发布者

case .finished:
cancellable?.cancel()

但是，如果发布者是一次性发布者，则cancel行是冗余的。当发布者发出finished时，管道终止。