提问人：Swift 提问时间：6/6/2022 更新时间：6/6/2022 访问量：463
无法在 swift 中检查具有“null”值的开关案例
Unable to check Switch cases with "null" value in swift
问：
检查我正在使用的多个条件switch statements
代码：这里所有情况都工作正常，但是。如果user_details？.rating = “” 是空的，那么我需要显示默认大小写，我的意思是所有星星都是空的，但它会进入 case _，user_details在哪里？。额定值？？“” <= “1.9” 为什么？
如果我强制解包，那么应用程序在到达此位置时会崩溃case _ where (user_details?.rating)! <= "1.9":
user_details？.rating = “” 那么如何显示所有星星为空
请指导我
switch user_details?.rating{
case "1.0":
star1.image = UIImage(named: "star")
star2.image = UIImage(named: "staremp")
star3.image = UIImage(named: "staremp")
star4.image = UIImage(named: "staremp")
star5.image = UIImage(named: "staremp")
break
case _ where user_details?.rating ?? "" <= "1.9":
star1.image = UIImage(named: "star")
star2.image = UIImage(named: "star-half")
star3.image = UIImage(named: "staremp")
star4.image = UIImage(named: "staremp")
star5.image = UIImage(named: "staremp")
break
case "2.0":
star1.image = UIImage(named: "star")
star2.image = UIImage(named: "star")
star3.image = UIImage(named: "staremp")
star4.image = UIImage(named: "staremp")
star5.image = UIImage(named: "staremp")
break
case _ where user_details?.rating ?? "" <= "2.9":
star1.image = UIImage(named: "star")
star2.image = UIImage(named: "star")
star3.image = UIImage(named: "star-half")
star4.image = UIImage(named: "staremp")
star5.image = UIImage(named: "staremp")
break
default:
star1.image = UIImage(named: "staremp")
star2.image = UIImage(named: "staremp")
star3.image = UIImage(named: "staremp")
star4.image = UIImage(named: "staremp")
star5.image = UIImage(named: "staremp")
break
}
答：
1赞
Timmy
6/6/2022
#1
应用程序崩溃了，因为你基本上是说：这个属性持有一个不是零的值，如果我错了，应用程序就会崩溃。force unwrappinguser_details?.rating
尝试在 switch 语句之前安全地解包：user_details?.rating
用：
if letif let rating = user_details?.rating { }else { }用：
guard letguard let rating = user_details?.rating else { return }提供默认值：
let rating = user_details?.rating ?? ""
然后，您的代码将如下所示：
guard let rating = user_details?.rating else {
//do something if it is nil
return
}
switch rating {
case "1.0":
star1.image = UIImage(named: "star")
star2.image = UIImage(named: "staremp")
star3.image = UIImage(named: "staremp")
star4.image = UIImage(named: "staremp")
star5.image = UIImage(named: "staremp")
break
case _ where user_details?.rating ?? "" <= "1.9":
star1.image = UIImage(named: "star")
star2.image = UIImage(named: "star-half")
star3.image = UIImage(named: "staremp")
star4.image = UIImage(named: "staremp")
star5.image = UIImage(named: "staremp")
break
case "2.0":
star1.image = UIImage(named: "star")
star2.image = UIImage(named: "star")
star3.image = UIImage(named: "staremp")
star4.image = UIImage(named: "staremp")
star5.image = UIImage(named: "staremp")
break
case _ where user_details?.rating ?? "" <= "2.9":
star1.image = UIImage(named: "star")
star2.image = UIImage(named: "star")
star3.image = UIImage(named: "star-half")
star4.image = UIImage(named: "staremp")
star5.image = UIImage(named: "staremp")
break
default:
star1.image = UIImage(named: "staremp")
star2.image = UIImage(named: "staremp")
star3.image = UIImage(named: "staremp")
star4.image = UIImage(named: "staremp")
star5.image = UIImage(named: "staremp")
break
}
评论
rating"" <= "1.9"trueuser_details?.rating ?? "" <= "1.9" && user_details?.rating ?? "" != ""let starCount = Double(user_details?.rating) ) ?? 0breakcase