我如何确定两个NSDate值之间的天数（同时考虑时间）？
NSDate值以[NSDate date]的形式呈现。
具体地说，当用户在我的iPhone应用程序中进入非活动状态时，我存储以下数值：
exitDate = [NSDate date];
当他们重新打开应用程序时，我获取当前时间：
NSDate *now = [NSDate date];
现在我想要实现以下内容：
-(int)numberOfDaysBetweenStartDate:exitDate andEndDate:now
下面是我使用的一个实现方法，用于确定两个日期之间的日历天数：
+ (NSInteger)daysBetweenDate:(NSDate*)fromDateTime andDate:(NSDate*)toDateTime
{
NSDate *fromDate;
NSDate *toDate;
NSCalendar *calendar = [NSCalendar currentCalendar];
[calendar rangeOfUnit:NSCalendarUnitDay startDate:&fromDate
interval:NULL forDate:fromDateTime];
[calendar rangeOfUnit:NSCalendarUnitDay startDate:&toDate
interval:NULL forDate:toDateTime];
NSDateComponents *difference = [calendar components:NSCalendarUnitDay
fromDate:fromDate toDate:toDate options:0];
return [difference day];
}
编辑：
上面提供了一种精彩的解决方案，这里是Swift版本，作为NSDate的扩展：
extension NSDate {
func numberOfDaysUntilDateTime(toDateTime: NSDate, inTimeZone timeZone: NSTimeZone? = nil) -> Int {
let calendar = NSCalendar.currentCalendar()
if let timeZone = timeZone {
calendar.timeZone = timeZone
}
var fromDate: NSDate?, toDate: NSDate?
calendar.rangeOfUnit(.Day, startDate: &fromDate, interval: nil, forDate: self)
calendar.rangeOfUnit(.Day, startDate: &toDate, interval: nil, forDate: toDateTime)
let difference = calendar.components(.Day, fromDate: fromDate!, toDate: toDate!, options: [])
return difference.day
}
}
如果根据使用情况需要的话，你可能需要删除一些强制解包操作。
上述解决方案也适用于除当前时区以外的时区，非常适合应用程序显示世界各地地点信息的场景。
这是我找到的最佳解决方案。似乎利用了苹果批准的方法来确定两个NSDate之间的任意单位数量。
- (NSInteger)daysBetween:(NSDate *)dt1 and:(NSDate *)dt2
{
NSUInteger unitFlags = NSCalendarUnitDay;
NSCalendar *calendar = [[NSCalendar alloc] initWithCalendarIdentifier:NSCalendarIdentifierGregorian];
NSDateComponents *components = [calendar components:unitFlags fromDate:dt1 toDate:dt2 options:0];
return [components day] + 1;
}
return [components day]+1; 改为 return ABS([components day])+1;，以防止负值时计算错误的天数。 - Tek YinSwift 3.0 更新
extension Date {
func differenceInDaysWithDate(date: Date) -> Int {
let calendar = Calendar.current
let date1 = calendar.startOfDay(for: self)
let date2 = calendar.startOfDay(for: date)
let components = calendar.dateComponents([.day], from: date1, to: date2)
return components.day ?? 0
}
}
Swift 2.0 更新
extension NSDate {
func differenceInDaysWithDate(date: NSDate) -> Int {
let calendar: NSCalendar = NSCalendar.currentCalendar()
let date1 = calendar.startOfDayForDate(self)
let date2 = calendar.startOfDayForDate(date)
let components = calendar.components(.Day, fromDate: date1, toDate: date2, options: [])
return components.day
}
}
原始解决方案
以下是Swift中的另一种解决方案。
如果您的目的是获取两个日期之间的确切天数，您可以像这样解决此问题：
// Assuming that firstDate and secondDate are defined
// ...
var calendar: NSCalendar = NSCalendar.currentCalendar()
// Replace the hour (time) of both dates with 00:00
let date1 = calendar.startOfDayForDate(firstDate)
let date2 = calendar.startOfDayForDate(secondDate)
let flags = NSCalendarUnit.DayCalendarUnit
let components = calendar.components(flags, fromDate: date1, toDate: date2, options: nil)
components.day // This will return the number of day(s) between dates
rangeOfUnit更简短、更简洁。但是（目前）需要注意的是，这需要iOS 8。 - nschumcalendar.startOfDayForDate。谢谢。 - Thomás Pereira我使用这个作为NSDate类的分类方法。
// returns number of days (absolute value) from another date (as number of midnights beween these dates)
- (int)daysFromDate:(NSDate *)pDate {
NSCalendar *calendar = [[NSCalendar alloc] initWithCalendarIdentifier:NSCalendarIdentifierGregorian];
NSInteger startDay=[calendar ordinalityOfUnit:NSCalendarUnitDay
inUnit:NSCalendarUnitEra
forDate:[NSDate date]];
NSInteger endDay=[calendar ordinalityOfUnit:NSCalendarUnitDay
inUnit:NSCalendarUnitEra
forDate:pDate];
return abs(endDay-startDay);
}
我需要计算两个日期之间的天数，包括开始那一天。 例如，2012年2月14日至2012年2月16日之间的天数应该是3。
+ (NSInteger)daysBetween:(NSDate *)dt1 and:(NSDate *)dt2 {
NSUInteger unitFlags = NSDayCalendarUnit;
NSCalendar* calendar = [NSCalendar currentCalendar];
NSDateComponents *components = [calendar components:unitFlags fromDate:dt1 toDate:dt2 options:0];
NSInteger daysBetween = abs([components day]);
return daysBetween+1;
}
NSDate *lastDate = [NSDate date];
NSDate *todaysDate = [NSDate date];
NSTimeInterval lastDiff = [lastDate timeIntervalSinceNow];
NSTimeInterval todaysDiff = [todaysDate timeIntervalSinceNow];
NSTimeInterval dateDiff = lastDiff - todaysDiff;
dateDiff将是两个日期之间的秒数。只需除以一天中的秒数即可。
@Brian
虽然Brian的答案不错，但只计算24小时块的天数差异，而不是日历天数差异。例如，在12月24日23:59离圣诞节仅有1分钟，对于许多应用程序来说，仍然被认为是同一天。Brian的daysBetween函数将返回0。
借鉴Brian原始实现和一天的开始/结束，我在我的程序中使用以下内容：(NSDate beginning of day and end of day)
- (NSDate *)beginningOfDay:(NSDate *)date
{
NSCalendar *cal = [NSCalendar currentCalendar];
NSDateComponents *components = [cal components:( NSDayCalendarUnit | NSMonthCalendarUnit | NSYearCalendarUnit | NSHourCalendarUnit | NSMinuteCalendarUnit | NSSecondCalendarUnit ) fromDate:date];
[components setHour:0];
[components setMinute:0];
[components setSecond:0];
return [cal dateFromComponents:components];
}
- (NSDate *)endOfDay:(NSDate *)date
{
NSCalendar *cal = [NSCalendar currentCalendar];
NSDateComponents *components = [cal components:( NSDayCalendarUnit | NSMonthCalendarUnit | NSYearCalendarUnit | NSHourCalendarUnit | NSMinuteCalendarUnit | NSSecondCalendarUnit ) fromDate:date];
[components setHour:23];
[components setMinute:59];
[components setSecond:59];
return [cal dateFromComponents:components];
}
- (int)daysBetween:(NSDate *)date1 and:(NSDate *)date2 {
NSDate *beginningOfDate1 = [self beginningOfDay:date1];
NSDate *endOfDate1 = [self endOfDay:date1];
NSCalendar *calendar = [[NSCalendar alloc] initWithCalendarIdentifier:NSGregorianCalendar];
NSDateComponents *beginningDayDiff = [calendar components:NSDayCalendarUnit fromDate:beginningOfDate1 toDate:date2 options:0];
NSDateComponents *endDayDiff = [calendar components:NSDayCalendarUnit fromDate:endOfDate1 toDate:date2 options:0];
if (beginningDayDiff.day > 0)
return beginningDayDiff.day;
else if (endDayDiff.day < 0)
return endDayDiff.day;
else {
return 0;
}
}
另一种方法：
NSDateFormatter* dayFmt = [[NSDateFormatter alloc] init];
[dayFmt setTimeZone:<whatever time zone you want>];
[dayFmt setDateFormat:@"g"];
NSInteger firstDay = [[dayFmt stringFromDate:firstDate] integerValue];
NSInteger secondDay = [[dayFmt stringFromDate:secondDate] integerValue];
NSInteger difference = secondDay - firstDay;
这是Brian函数在Swift中的实现：
class func daysBetweenThisDate(fromDateTime:NSDate, andThisDate toDateTime:NSDate)->Int?{
var fromDate:NSDate? = nil
var toDate:NSDate? = nil
let calendar = NSCalendar.currentCalendar()
calendar.rangeOfUnit(NSCalendarUnit.DayCalendarUnit, startDate: &fromDate, interval: nil, forDate: fromDateTime)
calendar.rangeOfUnit(NSCalendarUnit.DayCalendarUnit, startDate: &toDate, interval: nil, forDate: toDateTime)
if let from = fromDate {
if let to = toDate {
let difference = calendar.components(NSCalendarUnit.DayCalendarUnit, fromDate: from, toDate: to, options: NSCalendarOptions.allZeros)
return difference.day
}
}
return nil
}
对于那些想在Swift中实现此操作的访问此页面的人，我帮你们添加一个答案。方法基本相同。
private class func getDaysBetweenDates(startDate:NSDate, endDate:NSDate) -> NSInteger {
var gregorian: NSCalendar = NSCalendar.currentCalendar();
let flags = NSCalendarUnit.DayCalendarUnit
let components = gregorian.components(flags, fromDate: startDate, toDate: endDate, options: nil)
return components.day
}
这个答案可以在以下方法的讨论部分找到：
components(_:fromDate:toDate:options:)
rangeOfUnit：...来完成的），结果将为0（因为2h < 1 day）。 - Daniel Rinser