如何在 Swift Combine 中创建自定义链？答案

【问题标题】：How to create a custom chain in Swift Combine?如何在 Swift Combine 中创建自定义链？
【发布时间】：2020-09-30 02:24:23
【问题描述】：

我正在尝试为 Combine 创建一个 LocationManager 包装器。我有一个发布者和一些触发发布者的功能。但是，我想将它们与自定义命令组合在一起。

这是我目前得到的：

@available(OSX 10.15, iOS 13, tvOS 13, watchOS 6, *)
public class LocationProxy: NSObject {
    private lazy var manager = CLLocationManager()

    private static let authorizationSubject = PassthroughSubject<Bool, Never>()
    public private(set) lazy var authorizationPublisher: AnyPublisher<Bool, Never> = Self.authorizationSubject.eraseToAnyPublisher()

    var isAuthorized: Bool { CLLocationManager.isAuthorized }

    func isAuthorized(for type: LocationAPI.AuthorizationType) -> Bool {
        guard CLLocationManager.locationServicesEnabled() else { return false }

        #if os(macOS)
        return type == .always && CLLocationManager.authorizationStatus() == .authorizedAlways
        #else
        return (type == .whenInUse && CLLocationManager.authorizationStatus() == .authorizedWhenInUse)
            || (type == .always && CLLocationManager.authorizationStatus() == .authorizedAlways)
        #endif
    }

    func requestAuthorization(for type: LocationAPI.AuthorizationType = .whenInUse) {
        // Handle authorized and exit
        guard !isAuthorized(for: type) else {
            Self.authorizationSubject.send(true)
            return
        }

        // Request appropiate authorization before exit
        defer {
            #if os(macOS)
            if #available(OSX 10.15, *) {
                manager.requestAlwaysAuthorization()
            }
            #elseif os(tvOS)
            manager.requestWhenInUseAuthorization()
            #else
            switch type {
            case .whenInUse:
                manager.requestWhenInUseAuthorization()
            case .always:
                manager.requestAlwaysAuthorization()
            }
            #endif
        }

        // Handle mismatched allowed and exit
        guard !isAuthorized else {
            // Process callback in case authorization dialog not launched by OS
            // since user will be notified first time only and ignored subsequently
            Self.authorizationSubject.send(false)
            return
        }

        // Handle denied and exit
        guard CLLocationManager.authorizationStatus() == .notDetermined else {
            Self.authorizationSubject.send(false)
            return
        }
    }

    public func locationManager(_ manager: CLLocationManager, didChangeAuthorization status: CLAuthorizationStatus) {
        guard status != .notDetermined else { return }
        Self.authorizationSubject.send(isAuthorized)
    }
}

要使用它，我必须先订阅，然后调用请求授权函数：

cancellable = locationProxy.authorizationPublisher
    .sink { status in
        print(status)
    }

locationProxy.requestAuthorization()

有没有办法在一次调用中构造代码以订阅和请求授权，如下所示：

cancellable = locationProxy.authorizationPublisher
    .sink { status in
        print(status)
    }
    .requestAuthorization()

【问题讨论】：

标签： swift location reactive-programming combine

【解决方案1】：

您的requestAuthorization 应该返回发布者：

func requestAuthorization(for type: LocationAPI.AuthorizationType = .whenInUse) -> AnyPublisher<Bool, Never> {
  // start authorization flow

  return authorizationPublisher
}

我还建议您使用CurrentValueSubject 而不是PassthroughSubject，这样您在订阅authorizationPublisher 时始终可以获得“当前”状态。

【讨论】：