有一个名称类似的主题,但由于用户错误,该示例是一个错误。我相信这个例子是一个实际的XCode问题。
我正在遵循一个树屋教程,本着 swift 2.0 的精神,我在初始值设定项中使用了 guard 语句而不是 if let。我的代码与指令相同,除了使用了 guard 语句。它有一个错误,说"从初始值设定项返回而不初始化所有存储的属性"。一旦我将其更改为 if let 语句,它就起作用了。也许我在某处犯了一个错误,但我盯着它看了至少一个小时,没有未初始化的属性。
为了以防万一,我在 else 子句中将属性等于 nil,但这不会影响任何事情。
结构 每日天气 {
let maxTemp: Int?
let minTemp: Int?
let humidity: Int?
let precipChance: Int?
var summary: String?
var icon: UIImage? = UIImage(named: "default.png")
var largeIcon: UIImage? = UIImage(named: "default_large.png")
var sunriseTime: String?
var sunsetTime: String?
var day: String?
let dateFormatter = NSDateFormatter()
init(dailyWeatherDictionary: [String:AnyObject]) {
minTemp = dailyWeatherDictionary["temperatureMin"] as? Int
maxTemp = dailyWeatherDictionary["temperatureMax"] as? Int
guard let humidityFloat = dailyWeatherDictionary["humidity"] as? Double else { humidity = nil ; return }
humidity = Int(humidityFloat * 100)
guard let precipFloat = dailyWeatherDictionary["precipProbability"] as? Double else { precipChance = nil ; return }
precipChance = Int(precipFloat * 100)
summary = dailyWeatherDictionary["summary"] as? String
guard let
iconString = dailyWeatherDictionary["icon"] as? String,
iconEnum = Icon(rawValue: iconString) else { icon = nil ; largeIcon = nil ; return }
(icon, largeIcon) = iconEnum.toImage()
guard let sunriseDate = dailyWeatherDictionary["sunriseTime"] as? Double else { sunriseTime = nil ; return }
sunriseTime = timeStringFromUnixTime(sunriseDate)
guard let sunsetDate = dailyWeatherDictionary["sunsetTime"] as? Double else { sunsetTime = nil ; return }
sunsetTime = timeStringFromUnixTime(sunsetDate)
guard let time = dailyWeatherDictionary["time"] as? Double else { day = nil ; return }
day = dayStringFromUnixTime(time)
}
func timeStringFromUnixTime(unixTime: Double) -> String {
let date = NSDate(timeIntervalSince1970: unixTime)
dateFormatter.dateFormat = "hh:mm a"
return dateFormatter.stringFromDate(date)
}
func dayStringFromUnixTime(unixTime: Double) -> String {
let date = NSDate(timeIntervalSince1970: unixTime)
dateFormatter.locale = NSLocale(localeIdentifier: NSLocale.currentLocale().localeIdentifier)
dateFormatter.dateFormat = "EEEE"
return dateFormatter.stringFromDate(date)
}
}
让我们有
struct S {
var i: Int?
init(b: Bool){
guard b == false else { return }
//if b == true { return }
i = 0 // if b == true, this statement doesn't execute
}
}
let s1 = S(b: true)
let s2 = S(b: false)
print(s1, s2) // S(i: nil) S(i: Optional(0))
由于var i: Int?
具有默认值 nil,即使如果 init 的参数为 true i = 0
则无法访问,编译器也不会抱怨。
struct S {
let i: Int?
init(b: Bool){
guard b == false else { return }
//if b == true { return }
i = 0 // if b == true, this statement doesn't execute
}
}
不会编译,使用 error: return from initializer without initializing all stored properties
和 note: 'self.i' not initialized
,因为常量let i: Int?
没有任何默认值
你的麻烦是,你从初始化回来。通常,如果您的初始值设定项不可失败/初始化,请避免从初始值设定项返回?/.万一可失败的初始化?唯一接受的返回值为 NIL。