在 Swift 3 中获取时差

Question

我试图从这个guide 获取两个日期的时差。我不确定为dateComponents 参数输入什么。当我直接传入[.hour, .minute]时，会报错：

Playground execution failed: error: MyPlayground.playground:10:46: error: type of expression is ambiguous without more context
let timeDifference = calendar.dateComponents([.hour, .minute], from: stopTime!, to: date!)
                                             ^~~~~~~~~~~~~~~~

```

我首先尝试将其声明为常量，但不确定类型是什么。参数的类型为Set<Calendar.Component>，但当我尝试说它是向上Component、DateComponent 或CalendarComponent 时出现错误。

````

let timeFormatter = DateFormatter()
timeFormatter.dateFormat = "hh:mm a "
let time = "12:03 pm"
let stopTime = timeFormatter.date(from: time)

let date = Date()
let calendar = Calendar.current

let components:[DateComponent] = [.hour, .minute]
let timeDifference = calendar.dateComponents(components, from: stopTime!, to: date!)

Answer 1

dateComponents(_:from:to:) 方法声明如下：

public func dateComponents(_ components: Set<Calendar.Component>, 
    from start: Date, to end: Date) -> DateComponents

第一个参数是Set<Calendar.Components> 类型，但您似乎提供了[DateComponents]。这就是您看到错误的原因。

因此，应该这样做：

let components:[Calendar.Component] = [.hour, .minute]
let timeDifference = calendar.dateComponents(Set<Calendar.Component>(components), 
    from: stopTime!, to: date)

首先，我将数组的类型更改为[Calendar.Component]。其次，在将components 传递给方法之前，我创建了一个Set<Calendar.Component>。另一件事是你写了date!。 ! 是多余的，因为 date 已经是非可选的。无需拆包！

或者，您可以完全删除 components 变量！

let timeDifference = calendar.dateComponents([.hour, .minute], 
    from: stopTime!, to: date)

现在可以正常编译了！

但是，这可能不会产生您预期的结果，因为 timeFormatter.date(from: time) 产生的日期是 2000 年。我得到了这个非常肮脏的解决方案，但它仍然有效：

let timeFormatter = DateFormatter()
timeFormatter.dateFormat = "hh:mm a"
let time = "08:00 pm"
var stopTime = timeFormatter.date(from: time)

let date = Date()
let calendar = Calendar.current

let year = calendar.component(.year, from: date)
let month = calendar.component(.month, from: date)
let day = calendar.component(.day, from: date)
let hour = calendar.component(.hour, from: stopTime!)
let minute = calendar.component(.minute, from: stopTime!)

stopTime = calendar.date(bySetting: .year, value: year, of: stopTime!)
stopTime = calendar.date(bySetting: .month, value: month, of: stopTime!)
stopTime = calendar.date(bySetting: .day, value: day, of: stopTime!)
stopTime = calendar.date(bySetting: .hour, value: hour, of: stopTime!)
stopTime = calendar.date(bySetting: .minute, value: minute, of: stopTime!)

let timeDifference = calendar.dateComponents([.hour, .minute], from: stopTime!, to: date)

Answer 2

Swift 3.0

let start = Date();
//Your functions..
let end = Date();
print("Time to do something: \(end.timeIntervalSince(start)) seconds");