ios - 函数返回值为空 : Why?

Question

在 QueryHK 类中，我运行 HealthKit 查询以获取步骤和相应的日期。我想将这些数据写入 NSArray 并返回它，以便我可以调用 ViewController 中的函数。

• 问题:ViewController 中的代码没有返回任何内容，也没有错误。为什么返回是空的？

在我看来，查询并没有“写入返回”。

QueryHK.swift:

import UIKit
import HealthKit

class QueryHK: NSObject {

var steps = Double()
var date = NSDate()

func performHKQuery () -> (steps: Double, date: NSDate){

    let healthKitManager = HealthKitManager.sharedInstance
    let stepsSample = HKQuantityType.quantityTypeForIdentifier(HKQuantityTypeIdentifierStepCount)
    let stepsUnit = HKUnit.countUnit()
    let sampleQuery = HKSampleQuery(
        sampleType: stepsSample,
        predicate: nil,
        limit: 0,
        sortDescriptors: nil)
        {
            (sampleQuery, samples, error) in

            for sample in samples as [HKQuantitySample]
            {

                self.steps  = sample.quantity.doubleValueForUnit(stepsUnit)
                self.date  = sample.startDate

                println("Query HealthKit steps: \(self.steps)")
                println("Query HealthKit date: \(self.date)")

            }
    }
    healthKitManager.healthStore.executeQuery(sampleQuery)
    return (steps, date)
}
}

ViewController.swift:

import UIKit

class ViewController: UIViewController {

    var query = QueryHK()

    override func viewDidLoad() {
        super.viewDidLoad()

        printStepsAndDate()
    }


    func printStepsAndDate() {

    println(query.performHKQuery().date)
    println(query.performHKQuery().steps)

    }
}

Answer 1

原因是 HKSampleQuery 是异步处理的 - 它立即返回并在后台工作。因此，您的方法立即完成执行，而不是在结果处理程序 block 中处理响应。您需要更新您的方法以采用完成 block 而不是返回值。

QueryHK.swift:

import UIKit
import HealthKit

struct Sample {
    let step: Double
    let date: NSDate
}

class QueryHK: NSObject {

func performHKQuery(completion: (samples: [Sample]) -> Void) {

    let healthKitManager = HealthKitManager.sharedInstance
    let stepsSample = HKQuantityType.quantityTypeForIdentifier(HKQuantityTypeIdentifierStepCount)
    let stepsUnit = HKUnit.countUnit()
    let sampleQuery = HKSampleQuery(
        sampleType: stepsSample,
        predicate: nil,
        limit: 0,
        sortDescriptors: nil)
        {
            (sampleQuery, samples, error) in

            var processedSamples = [Sample]()
            for sample in samples as [HKQuantitySample]
            {
                processedSamples.append(Sample(step: sample.quantity.doubleValueForUnit(stepsUnit), date: sample.startDate))

                println("Query HealthKit steps: \(processedSamples.last?.step)")
                println("Query HealthKit date: \(processedSamples.last?.date)")
            }
            // Call the completion handler with the results here
            completion(samples: processedSamples)
    }
    healthKitManager.healthStore.executeQuery(sampleQuery)
}
}

ViewController.swift:

import UIKit

class ViewController: UIViewController {

    var query = QueryHK()

    override func viewDidLoad() {
        super.viewDidLoad()

        printStepsAndDate()
    }


    func printStepsAndDate() {
        query.performHKQuery() { steps in
            println(steps)
        }
    }
}