Swift 从 URLSession.shared.dataTaskPublisher 合并 Return Int

Question

我有以下代码进行 API 调用，接收数据并将其分配给 Core Data 托管对象。这很好用，并更新了我的数据。

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 return 作为此调用的结果 return 编辑和解码的对象数量。如果失败，我 return 0。本质上，我想要这个：

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'
}

我如何 return 作为网络调用的结果收到的对象计数？

Answer 1

我的建议是解码数据并在管道和 return 发布者中创建核心数据记录。在另一个函数中订阅发布者和 sink 项目数 and/or 处理错误。

我没有你的自定义物品，你得妥善管理self

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()
}

不过你也可以使用 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
}

或者一个iOS13兼容的async版本，这里perform可以异步

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()
    }
}

Swift 从 URLSession.shared.dataTaskPublisher 合并 Return Int

Swift Combine Return Int From URLSession.shared.dataTaskPublisher

swift

combine