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ios - 如何解开剩余的秒数以防止它为零？

问题描述

为什么我在展开 Optional 值时得到“意外发现 nil？我检查了 timerSeconds 的值，它被正确地分配给了我想要分配的值。但是，当我调用函数 StartTimer 时，我的应用程序崩溃了。

300 EggTimer/ViewController.swift:30: 致命错误：在展开可选值时意外发现 nil 2021-06-02 19:17:04.380375+1000 EggTimer[27674:932041] EggTimer/ViewController.swift:30: 致命错误：意外在展开可选值 (lldb) 时发现 nil

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()
          }
        }
     
    }

}

标签： iosswiftdictionaryswift-optionals

解决方案

请注意，在startTimer,self.secondsRemaining中与参数 不是指同一事物secondsRemaining：

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 {

一个简单的解决方法是在开始时设置self.secondsRemaining参数：secondsRemainingstartTimer

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

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