iOS 并发问题 : method returned before got the pedometer data

Question

像下面的代码，当我想通过一个方便的方法返回一个计步器数据时，但是方法返回早于数据被检索。我认为这可能是一个并发问题。如何以正确的方式返回数据以供将来使用？Thx

 func queryPedometerTodayTotalData() -> Int {
     var pedometerDataOfToday: CMPedometerData?
        self.queryPedometerDataFromDate(NSDate.today()!, toDate: NSDate(), withHandler: { (pedometerData, error) in
            pedometerDataOfToday = pedometerData!
            print("this print after got data in a background thread:\(pedometerDataOfToday)")
        })
        print("This should print before last print, and there haven't got the data now: \(pedometerDataOfToday)")
    return pedometerDataOfToday
}

Answer 1

关于并发问题，您是对的。您应该在 queryPedometerDataFromDate 的处理程序中使用结果。实现此目的的一种方法是为您的 queryPedometerTodayTotalData 方法使用完成 block ，而不是让它返回一个值，如下所示:

func queryPedometerTodayTotalData(completion:((CMPedometerData?)->())) {
    var pedometerDataOfToday: CMPedometerData?
    self.queryPedometerDataFromDate(NSDate.today()!, toDate: NSDate(), withHandler: { (pedometerData, error) in
        pedometerDataOfToday = pedometerData!
        completion(pedometerData)
    })
}

func testQueryPedometerTodayTotalData() {
    self.queryPedometerTodayTotalData { (data) in
        print(data)
    }
}