objective-c 如何从 NSDate 中减去小时数？
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How does one subtract hours from an NSDate?
提问by Georg Sch?lly
I would like to subtract 4 hours from a date. I read the date string into an NSDate object use the following code:
我想从日期中减去 4 小时。我使用以下代码将日期字符串读入 NSDate 对象：
NSDateFormatter * dateFormatter = [[[NSDateFormatter alloc] init] autorelease];
[dateFormatter setDateFormat:@"yyyy-MM-dd'T'HH:mm:ssZ"];
NSDate * mydate = [dateFormatter dateFromString:[dict objectForKey:@"published"]];
What do I do next?
我接下来该怎么做？
回答by Georg Sch?lly
NSDate *newDate = [theDate dateByAddingTimeInterval:-3600*4];
NSDate *newDate = [[[NSDate alloc] initWithTimeInterval:-3600*4
sinceDate:theDate]] autorelease];
回答by Chuck
NSCalendar is the general API for changing dates based on human time units. For this, you can use NSCalendar's -dateByAddingComponents:toDate:options:with a negative number of hours.
NSCalendar 是用于根据人类时间单位更改日期的通用 API。为此，您可以使用-dateByAddingComponents:toDate:options:带有负数小时数的NSCalendar 。
回答by Ben Packard
Since iOS 8 there is the more convenient dateByAddingUnit:
由于 iOS 8 有更方便的dateByAddingUnit：
Swift 2.x
斯威夫特 2.x
//subtract 3 hours
let calendar = NSCalendar.autoupdatingCurrentCalendar()
newDate = calendar.dateByAddingUnit(.Hour, value: -3, toDate: originalDate, options: [])
回答by Ning
//in Swift 3
//subtract 3 hours
let calendar = NSCalendar.autoupdatingCurrent
newDate = calendar.date(byAdding:.hour, value: -3, to: originalDate)
回答by Guillaume Laurent
In Swift 4 :
在 Swift 4 中：
var baseDate = ... // something
let dateMinus4Hours = Calendar.current.date(byAdding: .hour, value: -4, to: baseDate)
don't go with 24*3600and stuff, that's asking for trouble.
不要去24*3600和东西，那是自找麻烦。
回答by Pe Gra
Here a function which might be useful as it returns the date -4 h considering that this may also change the date and the month and eventually the year. the .searchBackward option is the important part :)
这是一个可能有用的函数，因为它返回日期 -4 小时，考虑到这也可能会更改日期和月份并最终更改年份。.searchBackward 选项是重要的部分:)
public static func correctSecondComponent(date: Date, calendar: Calendar = Calendar(identifier: Calendar.Identifier.gregorian))->Date {
let hour = calendar.component(.hour, from: date)
let e = (calendar as NSCalendar).date(byAdding: NSCalendar.Unit.hour, value: -4, to: date, options:.searchBackwards)!
return e
}
回答by Guvener Gokce
dateFromString function returns NSDate, not NSString. you should change,
dateFromString 函数返回 NSDate，而不是 NSString。你应该改变，
NSDate * theDate = [dateFormatter dateFromString:datetemp];
NSDate * theDate = [dateFormatter dateFromString:datetemp];
