ios - swift 错误 : value of optional type 'Double?' not unwrapped

Question

我是 Swift 的新手，这是什么错误:

let lvt=self?.lastVibrationTime
let delta=self!.deltaTime
let sens=self!.shakeSensitivity
let time:Double = CACurrentMediaTime()

//error is on `lvt` and says : Error:(37, 27) value of optional type 'Double?' not unwrapped; did you mean to use '!' or '?'?
if time - lvt > delta && data.userAcceleration.x < sens {
                    println("firmly shaken!")
                    self?.vibrateMe()
                }

Answer 1

当你写let lvt=self?.lastVibrationTime当使用self?你的lvt变量是可选的，你必须在使用它之前解包，你有很多解决方案修复此错误:

1. let lvt = self?.lastVibrationTime ?? 5 // 5 is the default value, you can use the value you want

2. let lvt = self!.lastVibrationTime

3. You can unwrap the value before use it:
if let lvt = self?.lastVibrationTime {
    // your code here...
}