我有以下代碼進行 API 呼叫、接收資料并將其分配給 Core Data 托管物件。這很好用，并更新了我的資料。
func importUsers(url: URL) {
URLSession.shared.dataTaskPublisher(for: url)
.map(\.data)
.sink(receiveCompletion: { completion in
if case .failure(let error) = completion {
print("DataImporter.runImport failed with error: \(error)")
}
}, receiveValue: { [weak self] data in
guard let self = self
else { return }
self.importContext.perform {
do {
// 2. Decode the response. This decodes directly to the Core Data Store
let users = try self.decoder.decode([GitUser].self, from: data)
try? self.importContext.save()
} catch {
print("DataImporter.runImport failed to decode json with error: \(error)")
}
}
})
.store(in: &self.cancellables) // store the returned cancellable in a property on `DataImporter`
}
但是，我需要回傳由于此呼叫而回傳和解碼的物件數。如果失敗，我回傳 0。本質上，我想要這個：
func importUsers(url: URL) -> Int {
URLSession.shared.dataTaskPublisher(for: url)
.map(\.data)
.sink(receiveCompletion: { completion in
if case .failure(let error) = completion {
print("DataImporter.runImport failed with error: \(error)")
}
}, receiveValue: { [weak self] data in
guard let self = self
else { return 0 }
var users: [GitUser] = []
self.importContext.perform {
do {
// 2. Decode the response. This decodes directly to the Core Data Store
users = try self.decoder.decode([GitUser].self, from: data)
try? self.importContext.save()
} catch {
print("DataImporter.runImport failed to decode json with error: \(error)")
}
}
return users.count
}).store(in: &self.cancellables) // error: Cannot convert return expression of type '()' to return type 'Int'
}
如何回傳由于網路呼叫而收到的物件數？
uj5u.com熱心網友回復：
我的建議是解碼資料并在管道中創建核心資料記錄并回傳發布者。在另一個函式中訂閱發布者和sink專案數和/或處理錯誤。
我沒有你的自定義物品，你要self好好管理
func importUsers(url: URL) -> AnyPublisher<Int,Error> {
URLSession.shared.dataTaskPublisher(for: url)
.map(\.data)
.tryMap{data -> Int in
var users: [GitUser] = []
var cdError : Error?
self.importContext.performAndWait {
do {
let users = try self.decoder.decode([GitUser].self, from: data)
try self.importContext.save()
} catch {
cdError = error
}
}
if let error = cdError { throw error }
return users.count
}
.eraseToAnyPublisher()
}
但是你也可以使用async/await
func importUsers(url: URL) async throws -> Int {
let (data, _) = try await URLSession.shared.data(from: url)
let users = try await self.importContext.perform {
try self.decoder.decode([GitUser].self, from: data)
try self.importContext.save()
}
return users.count
}
或者iOS 13兼容async版本，這里perform可以異步
func importUsers(url: URL) async throws -> Int {
try await withCheckedThrowingContinuation { continuation in
let task = URLSession.shared.dataTask(with: url) { [unowned self] (data, _ , error) in
if let error = error { continuation.resume(with: .failure(error)); return }
self.importContext.perform {
do {
let users = try self.decoder.decode([GitUser].self, from: data!)
try self.importContext.save()
continuation.resume(with: .success(users.count))
} catch {
continuation.resume(with: .failure(error))
}
}
}
task.resume()
}
}
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