ios - 事件指示器在异步查询结束前停止

Question

我有一个 ViewController，它调用一个类 HKQueryWeight，它运行一个 HealthKit 查询(顺便说一句，非常非常慢)并将数据保存到 CoreData。如果用户在查询结束前离开 VC，应用程序就会崩溃。

fatal error: unexpectedly found nil while unwrapping an Optional value (lldb)

最初我认为我可以通过添加一个 activityIndi​​cator 来修补这个问题，它在 viewDidAppear 中开始动画并在 VC 中的最后一个函数结束时停止。有用。但是，我相信，由于 healthKit 查询的异步特性，动画会在实际 healthKit 查询完成之前停止。

• 问题:如何创建动画仅在最后一个 healthKit 查询完成时停止的解决方案？

我不确定是否有必要提供代码，但我已经这样做了，以防有用

View Controller :

class ViewController: UIViewController {

    @IBOutlet var activityIndicator: UIActivityIndicatorView!

    override func viewDidAppear(animated: Bool) {
        super.viewDidAppear(animated)

        activityIndicator.startAnimating()

        setupArrays ()
    }

func setupArrays (){
    println("setting up arrays")

    if NSUserDefaults.standardUserDefaults().boolForKey("hrSwitch") == true {
        var hkQueryHeartRate = HKQueryHeartRate()
        hkQueryHeartRate.performHKQuery()
    }


    if NSUserDefaults.standardUserDefaults().boolForKey("weightSwitch") == true {
        var hkQueryWeight = HKQueryWeight()
        hkQueryWeight.performHKQuery()
    }

    self.activityIndicator.stopAnimating()
}

HKQuery

import Foundation
import CoreData
import HealthKit


class HKQueryWeight: HKQueryProtocol {


    func performHKQuery() {
        var appDel:AppDelegate = UIApplication.sharedApplication().delegate as AppDelegate
        var context = (UIApplication.sharedApplication().delegate as AppDelegate).managedObjectContext!

        let healthKitManager = HealthKitManager.sharedInstance
        let calendar = NSCalendar.currentCalendar()

        let interval = NSDateComponents()
        interval.day = 1

        // Set the anchor date to Monday at 3:00 a.m.
        let anchorComponents =
        calendar.components(.CalendarUnitDay | .CalendarUnitMonth |
            .CalendarUnitYear | .CalendarUnitWeekday, fromDate: NSDate())

        let offset = (7 + anchorComponents.weekday - 2) % 7
        anchorComponents.day -= offset
        anchorComponents.hour = 3
        //let now = NSDate()

        let anchorDate = calendar.dateFromComponents(anchorComponents)

        let quantityType = HKObjectType.quantityTypeForIdentifier(HKQuantityTypeIdentifierBodyMass)

        // Create the query
        let query = HKStatisticsCollectionQuery(quantityType: quantityType,
            quantitySamplePredicate: nil,
            options: .DiscreteAverage,
            anchorDate: anchorDate,
            intervalComponents: interval)

        // Set the results handler
        query.initialResultsHandler = {
            query, results, error in

            if error != nil {
                // Perform proper error handling here
                println("*** An error occurred while calculating the statistics: \(error.localizedDescription) ***")
                abort()
            }

            let endDate = NSDate()
            let startDate =
            calendar.dateByAddingUnit(.MonthCalendarUnit,
                value: -6, toDate: endDate, options: nil)

            // Plot the weekly step counts over the past 6 months
            results.enumerateStatisticsFromDate(startDate, toDate: endDate) {
                statistics, stop in

                if let quantity = statistics.averageQuantity() {
                    let date = statistics.startDate
                    let weight = quantity.doubleValueForUnit(HKUnit.gramUnitWithMetricPrefix(.Kilo))

                    println("weight date: \(date)")
                    println("weight value: \(weight)")


                    var weightData = NSEntityDescription.insertNewObjectForEntityForName("HKWeight", inManagedObjectContext: context) as HKWeight

                    //Saving to CoreData
                    weightData.setValue(weight, forKey: "weight_data")
                    weightData.setValue(date, forKey: "weight_date")

                    context.save(nil)

                }
            }
        }

        healthKitManager.healthStore.executeQuery(query)
    }
}

Answer 1

现在，调用查询后立即调用 self.activityIndi​​cator.stopAnimating()。由于查询是异步的，它们在被调用后仍然可以在后台执行一段时间，因此如果您在查询被调用后立即删除事件指示器，查询可能还不会完成。如果您希望事件指示器在您的查询完成后停止动画，您必须在您的异步查询 block 内调用它停止动画。

由于您的查询在不同的类中，您可以发布通知以在每个查询结束时结束事件指示器的动画，然后在第二个查询完成和第二个查询后停止 UIActivityIndi​​catorView 的动画收到通知，例如:

var notificationCount:Int = 0
var totalQueries = 0

func setupArrays (){
    println("setting up arrays")

    notificationCount = 0
    totalQueries = 0
    NSNotificationCenter.defaultCenter().addObserver(self, selector: "removeActivityIndicator", name:"ActivityIndicatorNotification", object: nil)

    if NSUserDefaults.standardUserDefaults().boolForKey("hrSwitch") == true {
        totalQueries = totalQueries + 1
        var hkQueryHeartRate = HKQueryHeartRate()
        hkQueryHeartRate.performHKQuery()
    }
    if NSUserDefaults.standardUserDefaults().boolForKey("weightSwitch") == true {
        totalQueries = totalQueries + 1
        var hkQueryWeight = HKQueryWeight()
        hkQueryWeight.performHKQuery()
    }

    if totalQueries == 0 {
        self.activityIndicator.stopAnimating()
    }
}

func removeActivityIndicator () {

    notificationCount = notificationCount + 1

    if notificationCount == totalQueries {

        dispatch_async(dispatch_get_main_queue()) {
            self.activityIndicator.stopAnimating()
            NSNotificationCenter.defaultCenter().removeObserver(self, name:"ActivityIndicatorNotification", object:nil)
        }
    }
}

然后在HKQueryWeight中:

func performHKQuery() {

    // ...All the code before the query...

    // Set the results handler
    query.initialResultsHandler = {
        query, results, error in

        //...All the code currently within your query...

        NSNotificationCenter.defaultCenter().postNotificationName("ActivityIndicatorNotification", object: nil) // <-- post notification to stop animating the activity indicator once the query's complete
    }