我怎样才能打开剩余的秒数以防止它为零？

Question

为什么我在展开可选值时收到“意外发现 nil？我检查了 timerSeconds 的值，它已正确分配给我想要分配给它的对象。但是，当我调用函数 StartTimer 我的应用程序时正在崩溃。

300 EggTimer/ViewController.swift:30: Fatal error: Unexpectedly found nil while unwrapping an Optional value 2021-06-02 19:17:04.380375+1000 EggTimer[27674:932041] EggTimer/ViewController.swift:30: Fatal error: Unexpectedly found nil while unwrapping an Optional value (lldb)

import UIKit

class ViewController: UIViewController {
    
let eggTimes : [String : Int] = ["Soft": 300, "Medium": 420, "Hard": 720]
var secondsRemaining: Int?
@IBAction func hardnessSelected(_ sender: UIButton) {
    let hardness = sender.currentTitle!
    let timerSeconds = eggTimes[hardness]!

    print(timerSeconds)
    //until here the code seems to work fine
    
    
    startTimer(secondsRemaining: timerSeconds)
    //call the function start timer and give the secondRemaining argument the value of timerSeconds
    
}
func startTimer (secondsRemaining: Int?){
//create a function called startTimer which accepts an interger as argument called secondsremaining
    Timer.scheduledTimer(withTimeInterval: 1.0, repeats: true) { (Timer) in
        if self.secondsRemaining! > 0 {
            //if the secondsRemaining >
            print ("\(self.secondsRemaining ?? 0) seconds")
            self.secondsRemaining! -= 1
        }else {
            Timer.invalidate()
          }
        }
     
    }

}

Answer 1

注意在startTimer中，self.secondsRemaining与参数secondsRemaining指的不是同一个东西：

var secondsRemaining: Int? // self.secondsRemaining

@IBAction func hardnessSelected(_ sender: UIButton) {
   ...
}
func startTimer (secondsRemaining: Int?){ // you never use this parameter
//create a function called startTimer which accepts an interger as argument called secondsremaining
    Timer.scheduledTimer(withTimeInterval: 1.0, repeats: true) { (Timer) in

        // here you are referring to the var declared outside of the methods
        // which you never assign anything to.
        // this does not refer to the parameter
        if self.secondsRemaining! > 0 {

一个简单的修复方法是将 self.secondsRemaining 设置为 startTimer 开头的参数 secondsRemaining:

func startTimer (secondsRemaining: Int?){ // you never use this parameter
    self.secondsRemaining = secondsRemaining
    Timer.scheduledTimer(withTimeInterval: 1.0, repeats: true) { (Timer) in
        // same as before...

Answer 2

您好@dumanji，您还使用 ! 强制解包了两个常量。如果您尝试使用零值，这可能会崩溃。特别是如果您计划将此应用程序推向生产环境，这可能会导致意外的运行时错误和应用程序崩溃。

示例：

设硬度=sender.currentTitle!
让 timerSeconds = eggTimes[硬度]!

考虑使用 ?? （nil 合并运算符）在常量右侧提供默认值，以防可选的 returns nil.

可能的方法：

让 timerSeconds = eggTimes[硬度] ?? 420

如果有帮助请告诉我。

我怎样才能打开剩余的秒数以防止它为零？

How can I unwrap seconds remaining to prevent it from being nil?

dictionary

ios

swift

swift-optionals