问题描述
为什么我会收到“在打开可选值时意外发现 nil?我检查了 timerSeconds 的值,它被正确分配给我想要分配给它的值。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:意外发现 解包可选值时为零 2021-06-02 19:17:04.380375+1000 EggTimer[27674:932041] EggTimer/ViewController.swift:30:致命错误: 解包可选值 (lldb) 时意外发现 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()
}
}
}
}
解决方法
请注意,在 startTimer
中,self.secondsRemaining
与参数 secondsRemaining
指代的不同:
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 self.secondsRemaining
的开头将 secondsRemaining
设置为参数 startTimer
:
func startTimer (secondsRemaining: Int?){ // you never use this parameter
self.secondsRemaining = secondsRemaining
Timer.scheduledTimer(withTimeInterval: 1.0,repeats: true) { (Timer) in
// same as before...
,
嗨@dumanji,您还使用 ! 强制解开两个常量。如果您尝试使用一个为零的值,这可能会崩溃。尤其是如果您打算将此应用推向生产,这可能会导致意外的运行时错误和应用崩溃。
示例:
- 让硬度 = 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,以防可选返回 nil。
可能的方法:
- 让 timerSeconds = eggTimes[硬度] ?? 420
如果这有帮助,请告诉我。