Swift: NSDate减去NSDate (小时)

Question

我在Swift中有一个模型，其中有一个名为NSDate的expirationDate字段，我希望根据当前的日期计算过期前的小时数。

有什么简单的方法可以用现有的NSDate功能来做到这一点呢？

Answer 1

现在不能检查，但应该是

expirationDate.timeIntervalSinceNow / 3600

Answer 2

只需在这两个日期(“现在”和“到期日期”)之间找到秒数(NSTimeInterval)，然后除以60*60 = 3600：

let secondsUntilExpiration = expirationDate.timeIntervalSinceDate(NSDate());

let hoursUntilExpiration = secondsUntilExpiration / 3600

例如：

  7> let now = NSDate() 
now: NSDate = 2016-02-01 03:44:06 UTC
  8> let expirationDate = now.dateByAddingTimeInterval(60*60*10) // ten hours from now
expirationDate: NSDate = 2016-02-01 13:44:06 UTC
  9> let secondsUntilExpiration = expirationDate.timeIntervalSinceDate(NSDate()); 
secondsUntilExpiration: NSTimeInterval = 35991.422316968441
 10> let hoursUntilExpiration = secondsUntilExpiration / 3600 
hoursUntilExpiration: Double = 9.9976173102690122 
// Slightly less than the 10 hours above because of the time it took me to type.