日期比较

有 4 种比较日期的方法：

迅速

• isEqualToDate(anotherDate: NSDate) -> Bool
• earlierDate(anotherDate: NSDate) -> NSDate
• laterDate(anotherDate: NSDate) -> NSDate
• compare(anotherDate: NSDate) -> NSComparisonResult

Objective-C

• - (BOOL)isEqualToDate:(NSDate *)anotherDate
• - (NSDate *)earlierDate:(NSDate *)anotherDate
• - (NSDate *)laterDate:(NSDate *)anotherDate
• - (NSComparisonResult)compare:(NSDate *)anotherDate

假设我们有 2 个日期：

迅速

let date1: NSDate = ... // initialized as  July 7, 2016 00:00:00
let date2: NSDate = ... // initialized as  July 2, 2016 00:00:00

Objective-C

NSDate *date1 = ... // initialized as  July 7, 2016 00:00:00
NSDate *date2 = ... // initialized as  July 2, 2016 00:00:00

然后，为了比较它们，我们尝试以下代码：

迅速

if date1.isEqualToDate(date2) {
    // returns false, as both dates aren't equal
}

earlierDate: NSDate = date1.earlierDate(date2) // returns the earlier date of the two (date 2)
laterDate: NSDate = date1.laterDate(date2) // returns the later date of the two (date1)

result: NSComparisonResult = date1.compare(date2)

if result == .OrderedAscending {
    // true if date1 is earlier than date2
} else if result == .OrderedSame {
    // true if the dates are the same
} else if result == .OrderedDescending {
    // true if date1 is later than date1
}

Objective-C

if ([date1 isEqualToDate:date2]) {
    // returns false, as both date are not equal
}

NSDate *earlierDate = [date1 earlierDate:date2]; // returns date which comes earlier from both date, here it will return date2
NSDate *laterDate = [date1 laterDate:date2]; // returns date which comes later from both date, here it will return date1

NSComparisonResult result = [date1 compare:date2];
if (result == NSOrderedAscending) {
    // fails
    // comes here if date1 is earlier then date2, in our case it will not come here
} else if (result == NSOrderedSame){
    // fails
    // comes here if date1 is same as date2, in our case it will not come here
} else{ // NSOrderedDescending
    // succeeds
    // comes here if date1 is later than date2, in our case it will come here
}

如果你想比较日期并处理秒，周，月和年：

Swift 3

let dateStringUTC = "2016-10-22 12:37:48 +0000"
let dateFormatter = DateFormatter()
dateFormatter.locale = Locale(identifier: "en_US_POSIX")
dateFormatter.dateFormat = "yyyy-MM-dd HH:mm:ss X"
let date = dateFormatter.date(from: dateStringUTC)!

let now = Date()

let formatter = DateComponentsFormatter()
formatter.unitsStyle = .full
formatter.maximumUnitCount = 2
let string = formatter.string(from: date, to: Date())! + " " + NSLocalizedString("ago", comment: "added after elapsed time to say how long before")

或者你可以为每个组件使用它：

// get the current date and time
let currentDateTime = Date()

// get the user's calendar
let userCalendar = Calendar.current

// choose which date and time components are needed
let requestedComponents: Set<Calendar.Component> = [
    .year,
    .month,
    .day,
    .hour,
    .minute,
    .second
]

// get the components
let dateTimeComponents = userCalendar.dateComponents(requestedComponents, from: currentDateTime)

// now the components are available
dateTimeComponents.year 
dateTimeComponents.month 
dateTimeComponents.day  
dateTimeComponents.hour 
dateTimeComponents.minute
dateTimeComponents.second