如何在带有 RxSwift 的驱动程序上使用 flatMapLatest

Posted 2023-03-10

【中文标题】如何在带有 RxSwift 的驱动程序上使用 flatMapLatest

【英文标题】：How to use flatMapLatest on a driver with RxSwift

【发布时间】：2019-02-09 12:38:08

【问题描述】：

每当我的用户位置发生变化时，我都会尝试从网络中获取一些数据。

struct CityService 
  private init() 

  static let shared = CityService()

  lazy var nearbyCities: Driver<[City]> = 
    return GeolocationService.instance.location
      .flatMapLatest( coordinate in
        let location = CLLocation(latitude: coordinate.latitude, longitude: coordinate.longitude)
        return CityService.shared.fetchNearbyCitiesFor(location)
      ).asDriver(onErrorJustReturn: [])
  ()

  func fetchNearbyCitiesFor(_ location: CLLocation) -> Observable<[City]> 
    return Observable.create  observer in
      let disposable = Disposables.create()

      // Mock a fetch from the network:
      let cities = [City(name: "Amsterdam"), City(name: "Berlin")]
      observer.onNext(cities)
      observer.on(.completed)

      return disposable
    
  


class GeolocationService 
  static let instance = GeolocationService()
  private (set) var location: Driver<CLLocationCoordinate2D>

// from: https://github.com/ReactiveX/RxSwift/blob/master/RxExample/RxExample/Services/GeolocationService.swift

struct City 
  let name: String

但是，这不是编译，原因是：

Cannot convert value of type 'SharedSequence<DriverSharingStrategy, [Any]>' to specified type 'Driver<[City]>'
(aka 'SharedSequence<DriverSharingStrategy, Array<City>>')

我还尝试添加一些类型提示以获得更好的错误：

lazy var nearbyCities: Driver<[City]> = 
  return GeolocationService.shared.location
  .flatMapLatest( coordinate -> Observable<[City]> in
    let location = CLLocation(latitude: coordinate.latitude, longitude: coordinate.longitude)
    let nearbyCities: Observable<[City]> = CityService.shared.fetchNearbyCitiesFor(location)
    return nearbyCities.catch
  ).asDriver(onErrorJustReturn: [City]())
()

但给我的只是：

Cannot convert value of type '(_) -> Observable<[City]>' to expected argument type '(CLLocationCoordinate2D) -> SharedSequence<_, _>'

我在这里做错了什么？

【参考方案1】：

您将.asDriver 呼叫置于错误的位置。

lazy var nearbyCities: Driver<[City]> = 
    return GeolocationService.instance.location
        .flatMapLatest( (coordinate) -> Driver<[City]> in
            let location = CLLocation(latitude: coordinate.latitude, longitude: coordinate.longitude)
            return CityService.shared.fetchNearbyCitiesFor(location)
                .asDriver(onErrorJustReturn: [])
        )
()

【讨论】：

啊！是的，最后。非常感谢。不过，我仍然无法完全理解 Drivers .. 任何与最新 RxSwift 保持同步的好资源？