爲什麼「打印到控制檯」比「.text into label」要快得多

Question

我試圖顯示CMPedometer的節奏和步速數據。當我使用連接的手機運行應用程序時，它會立即通過print("...")函數將數據輸出寫入控制檯，但需要多次轉動，直到它顯示UILabel中的數據。 如何儘可能快地獲取數據，以便我可以使用它們？

最佳，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

更新塊被稱爲後臺線程，你需要在主線程上更新UI。將UI更新調用包裹發送回主線程：

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)") 
     } 
    } 
}