Question

我正在开发第二个应用程序，学习Swift。我的第一个是一个计算器，当按下按钮时，该计算器根据许多UITextField输入输出一些结果。

我现在已经完成了一个倒计时计时器，通过在线教程进行操作。

如何使用UITextField中输入的数字设置持续时间（“秒”变量）？我尝试使用

var seconds = Double(timeSetupField.text!)!

代替

var seconds = 60

但是我知道这是行不通的，但是我不确定为什么。属性初始化程序在“自我”可用之前运行，但是我没有使用“自我”。 -我怀疑我误会了一些东西。变量的使用比我简单的计算器要复杂一些。

任何有关如何实现此建议的建议都是很好的，对上述问题的任何解释也将受到赞赏。

代码：

//
//  ViewController.swift
//  CountdownTimer
//
//  Created by Matt Baines on 01/09/2018.
//  Copyright © 2018 Matt Baines. All rights reserved.
//

import UIKit

class ViewController: UIViewController {
    // PROPERTIES
    @IBOutlet weak var timeSetupField: UITextField!
    @IBOutlet weak var timeCountdownLabel: UILabel!
    @IBOutlet weak var enterTimeLabel: UILabel!
    @IBOutlet weak var pauseButton: UIButton!
    @IBOutlet weak var startButton: UIButton!

    // DECLARATION OF VARIABLES
    // This variable will hold a starting value of seconds.
    var seconds = 60
    // Timer variable
    var timer = Timer()
    //This will be used to make sure only one timer is created at a time.
    var isTimerRunning = false
    // For pause & resume
    var resumeTapped = false

    override func viewDidLoad() {
        super.viewDidLoad()
        // Disable pause button so it is not visible until a time is started.
        pauseButton.isEnabled = false
    }

    func runTimer() {
        timer = Timer.scheduledTimer(timeInterval: 1, target: self,   selector:(#selector(ViewController.updateTimer)), userInfo: nil, repeats: true)
        isTimerRunning = true
        pauseButton.isEnabled = true
    }

    @objc func updateTimer() {
        if seconds < 1 {
            timer.invalidate()
        } else {
            // This will decrement the seconds.
            seconds -= 1
            // This will update the label.
            timeCountdownLabel.text = timeString(time: TimeInterval(seconds))
        }
    }

    func timeString(time:TimeInterval) -> String {
        let hours = Int(time) / 3600
        let minutes = Int(time) / 60 % 60
        let seconds = Int(time) % 60
        return String(format:"%02i:%02i:%02i", hours, minutes, seconds)
    }

    @IBAction func startButton(_ sender: UIButton) {
        if isTimerRunning == false {
            runTimer()
            self.startButton.isEnabled = false
        }
    }

    @IBAction func pauseButton(_ sender: UIButton) {
        if self.resumeTapped == false {
            timer.invalidate()
            self.resumeTapped = true
            self.pauseButton.setTitle("Resume", for: .normal)
        } else {
            runTimer()
            self.resumeTapped = false
            self.pauseButton.setTitle("Pause", for: .normal)
        }
    }

    @IBAction func resetButton(_ sender: UIButton) {
        timer.invalidate()
        // Manually enter the restarting point for the seconds
        seconds = 60
        timeCountdownLabel.text = timeString(time: TimeInterval(seconds))
        isTimerRunning = false
        // Ensure pause button text is set back to pause
        self.pauseButton.setTitle("Pause", for: .normal)
        pauseButton.isEnabled = false
        startButton.isEnabled = true
    }
}

Answer 1

您只是要替换代码行

var seconds = 60

与

var seconds = Double(timeSetupField.text!)!

您在哪里声明变量？如果是这种情况，这就是您的问题所在。

“ Self”（表示视图控制器）直到viewDidLoad才加载。在加载视图之前，您无法访问IBOutlets。您正试图从IBOutlet获取“尚不存在”的信息。

如果在情节提要中已经在timeSetupField上设置了一些文本，则可以执行以下操作：

//Global Variables
var seconds = 60

//Life cycle
override func viewDidLoad() {
    super.viewDidLoad()   
    pauseButton.isEnabled = false
    // Checks to make sure the timeSetupField.text isn't nil. If it is nil, you will not run any more code within viewDidLoad which prevents a crash on the next line if timeFromTextField is nil. 
    guard let timeFromTextField = timeSetupField.text else { return }
    seconds = timeFromTextField
}

此时，您的视图已加载，并且可以访问timeSetupField.text。您可以使用默认值全局声明秒数，以便可以在ViewController文件中的任何位置访问它，但是在插座可用后在ViewDidLoad中设置该值。

在这种情况下，您可以从代码中的任何函数（例如IBAction或在按下键盘上的Enter时调用的函数）中安全地更改秒变量。

Answer 2

您已经有了一个很好的开始，但是可以通过分离计时器逻辑和查看控制器代码来改进代码-这将使计时器更易于测试，并允许您在其他地方重用它。下面的代码不完整，但是可以正常工作，它将使您开始分离UI和逻辑。祝您第二个应用程序好运！

class ViewController: UIViewController {

    @IBOutlet weak var timeSetupField: UITextField!
    @IBOutlet weak var timeCountdownLabel: UILabel!
    @IBOutlet weak var pauseButton: UIButton!
    @IBOutlet weak var startButton: UIButton!
    var seconds = 60
    var timer: SecondsTimer?

    override func viewWillAppear(_ animated: Bool) {
        super.viewWillAppear(animated)
        updateTimeLabel(newSeconds: 60)
    }

    func updateTimeLabel(newSeconds: Int) {
        let hours = newSeconds / 3600
        let minutes = newSeconds / 60 % 60
        let seconds = newSeconds % 60
        let timeStr = String(format:"%02i:%02i:%02i", hours, minutes, seconds)
        timeCountdownLabel.text = timeStr
        timeCountdownLabel.sizeToFit()
    }

    @IBAction func startButton(_ sender: UIButton) {
        timer = SecondsTimer.init(callback: timerUpdate)
        timer?.start(initialSeconds: 60)
        self.startButton.isEnabled = false
    }

    private func timerUpdate(seconds: Int) {
        if seconds > 0 {
            updateTimeLabel(newSeconds: seconds)
        } else {
            timer?.stop()
        }
    }

    @IBAction func pauseButton(_ sender: UIButton) {
        guard let timer = timer else { return }
        if timer.paused {
            pauseButton.setTitle("Pause", for: .normal)
        } else {
            pauseButton.setTitle("Resume", for: .normal)
        }
        pauseButton.sizeToFit()
        timer.paused = !timer.paused
    }

    @IBAction func resetButton(_ sender: UIButton) {
        timer?.reset()
        updateTimeLabel(newSeconds: 60)
    }

}

class SecondsTimer: NSObject {
    var paused = false
    var stopReqest = false
    var seconds = 0
    let callback: (Int)->()

    init(callback: @escaping (Int)->()) {
        self.callback = callback
        super.init()
        NotificationCenter.default.addObserver(self, selector: #selector(SecondsTimer.applicationDidBecomeActiveNotification), name: NSNotification.Name.UIApplicationDidBecomeActive, object: nil)
        NotificationCenter.default.addObserver(self, selector: #selector(SecondsTimer.applicationWillResignActiveNotification), name: NSNotification.Name.UIApplicationWillResignActive, object: nil)
    }

    deinit {
        NotificationCenter.default.removeObserver(self, name: NSNotification.Name.UIApplicationDidBecomeActive, object: nil)
        NotificationCenter.default.removeObserver(self, name: NSNotification.Name.UIApplicationWillResignActive, object: nil)
        print("timer deinit")
    }

    func start(initialSeconds: Int = 60) {
        paused = false
        stopReqest = false
        seconds = initialSeconds
        Timer.scheduledTimer(timeInterval: 1.0, target: self, selector: #selector(self.deccrementSeconds), userInfo: nil, repeats: true)
    }

    @objc func reset() {
        seconds = 60
    }

    func stop() {
        stopReqest = true
    }

    @objc func applicationDidBecomeActiveNotification() {
        paused = false
    }

    @objc func applicationWillResignActiveNotification() {
        paused = true
    }

    @objc func deccrementSeconds(timer: Timer)  {
        if stopReqest {
            timer.invalidate()
            return
        }
        if paused == false {
            seconds -= 1
            callback(seconds)
        }
    }

}

使用uitextfield条目指定倒数计时器持续时间

2 个答案: