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swift - Swift Combine 转换一组发布者

问题描述

我正在通过组合位我似乎并没有围绕一些琐碎的操作。我正在构建一个基于执行一些 HealthKit 操作的组合。主要我有两个操作：

  1. func workouts(_ limit: Int) -> AnyPublisher<[HKWorkout], Error>
  2. func workoutDetails(_ workout: HKWorkout) -> AnyPublisher<WorkoutDetails, Error>

首先，我将使用第一个查询一些锻炼，这很容易。

HKHealthStore().workouts(HKObjectQueryNoLimit)
    .sink(receiveCompletion: { subject in
        switch subject {
        
        case .finished:
            break
        case .failure(let error):
            dump(error)
        }
    }, receiveValue: { workouts in
        dump(workouts)
        // What now? 
    }).store(in: &bag)

现在我想查询第二个函数。它将锻炼作为参数并返回有关HKWorkout. 如何使用返回的第二个函数查询第二个函数，[HKWorkout]但不知道如何处理。

到目前为止，我所尝试的都行不通。

HKHealthStore().workouts(HKObjectQueryNoLimit)
    .map({ workouts -> AnyPublisher<[WorkoutDetails], Never> in
        
        return workouts.publisher.flatMap({ workout in
            return Just(workout as! [WorkoutDetails]).eraseToAnyPublisher()
                .eraseToAnyPublisher()
        })
        .eraseToAnyPublisher()
        
    }).sink(receiveCompletion: { subs in
        switch subs {
        
        }
    }, receiveValue: { val in
        /// Cannot convert value of type 'AnyPublisher<[WorkoutDetails], Never>' to expected argument type 'Void'
        /// I am not able to get [WorkoutDetails] here as I'd like
        dump(val)
    })
    .store(in: &bag)

编辑：我终于使用的解决方案。有两个选项我终于设法使它工作并理解它。

一个是@New Dev 最终在sink组合数组中接收的答案，另一个是接收sink单个元素以保存在数组中。

HKHealthStore().workouts(HKObjectQueryNoLimit)
    .flatMap({
        $0.publisher.eraseToAnyPublisher()
    }).flatMap({
        $0.workoutWithDetails
    }).sink(receiveCompletion: { comp in
        switch comp {

        case .finished:
            break
        case .failure(let er):
            dump(er)
        }
    }, receiveValue: { details in
        /// Add the individual `WorkoutDetails` elements to an array 
        results.append(details)
    }).store(in: &SGHealthManager.bag)

标签： swiftcombine

解决方案

一般的做法是把flatMap数组变成Sequence单个值的发布者，然后对每个值（另一个flatMap）做任何异步操作，然后collect得到结果：

HKHealthStore()
   .workouts(HKObjectQueryNoLimit)
   .flatMap { workouts in workouts.publisher }
   .flatMap { workout in
       workoutDetails(workout)
   }
   .collect()
   .sink(
      receiveCompletion: { ... },
      receiveValue: { arrayOfWorkoutDetails in
          // arrayOfWorkoutDetails is of type [WorkoutDetails]
      })
   .store(in: &bag)

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