如何从NSDate中减去小时数？

Question

我想从约会中减去4个小时.我将日期字符串读入NSDate对象使用以下代码:

NSDateFormatter * dateFormatter = [[[NSDateFormatter alloc] init] autorelease];
[dateFormatter setDateFormat:@"yyyy-MM-dd'T'HH:mm:ssZ"];
NSDate * mydate = [dateFormatter dateFromString:[dict objectForKey:@"published"]];

接下来我该怎么办？

Answer 1

NSDate *newDate = [theDate dateByAddingTimeInterval:-3600*4];

链接到文档.

NSDate *newDate = [[[NSDate alloc] initWithTimeInterval:-3600*4
                                              sinceDate:theDate]] autorelease];

链接到文档.

Answer 2

NSCalendar是根据人工时间单位更改日期的通用API.为此,您可以使用-dateByAddingComponents:toDate:options:负数小时的NSCalendar .

Answer 3

在 Swift 4 中：

var baseDate = ... // something
let dateMinus4Hours = Calendar.current.date(byAdding: .hour, value: -4, to: baseDate)

不要去24*3600和东西，那是自找麻烦。

Answer 4

从iOS 8开始,更方便dateByAddingUnit:

Swift 2.x

//subtract 3 hours
let calendar = NSCalendar.autoupdatingCurrentCalendar()
newDate = calendar.dateByAddingUnit(.Hour, value: -3, toDate: originalDate, options: [])

Answer 5

//in Swift 3
//subtract 3 hours
let calendar = NSCalendar.autoupdatingCurrent
newDate = calendar.date(byAdding:.hour, value: -3, to: originalDate)