ios - 为什么 "print into console"比 ".text into label "快得多

Question

我正在尝试显示 CMPedometer 的节奏和配速数据。当我在连接手机的情况下运行该应用程序时，它会立即通过 print("...") 函数将数据输出写入控制台，但需要多次轮流才能将数据显示在UILabel。 我怎样才能尽快获取数据以便使用它们？

最好的，扎克

import UIKit
import CoreMotion

class ViewController: UIViewController {
    let pedometer = CMPedometer()
    @IBOutlet weak var paceLabel: UILabel!
    @IBOutlet weak var cadenceLabel: UILabel!

    override func viewDidLoad() {
        super.viewDidLoad()

        guard CMPedometer.isCadenceAvailable() && CMPedometer.isPaceAvailable() else{
            print("Pace and cadence data are not available")
            return
        }         
        let oneWeekAgo = NSDate(timeIntervalSinceNow: -(7 * 24 * 60 * 60))
        pedometer.startUpdates(from: oneWeekAgo as Date) {data, error in
            guard let pData = data , error == nil else{
                return
            }
            //The current pace of the user, measured in seconds per meter. (1 step = 83cm?)
            if let pace = pData.currentPace{
                print("Pace = \(pace)")
                self.paceLabel.text = "Pace = \(round(Double(pace))*10/10)"
            }
            //The rate at which steps are taken, measured in steps per second.
            if let cadence = pData.currentCadence{
                self.cadenceLabel.text = "Cadence = \(cadence))"
                print("Cadence = \(cadence)")
            }
        }// -----------------oneWeekAgo        
    }// -----------------ViewDidLoad

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
    }
}//-------------------- UIViewController

Answer 1

更新 block 在后台线程上调用，您需要在主线程上更新您的 UI。将 UI 更新调用打包回主线程:

Dispatch.main.async {
    //The current pace of the user, measured in seconds per meter. (1 step = 83cm?)
    if let pace = pData.currentPace{
        print("Pace = \(pace)")
        self.paceLabel.text = "Pace = \(round(Double(pace))*10/10)"
    }

    //The rate at which steps are taken, measured in steps per second.
    if let cadence = pData.currentCadence{
        self.cadenceLabel.text = "Cadence = \(cadence))"
            print("Cadence = \(cadence)")
        }
    }
}