How to convert NSDate in to relative format as “To

问题:

I want to convert nsdate in to relative format like "Today","Yesterday","a week ago","a month ago","a year ago","date as it is".

I have written following method for it.. but some how its just printing as it is date.. can you please tell me what should be the problem?

//Following is my function which converts the date into relative string

+(NSString *)getDateDiffrence:(NSDate *)strDate{
    NSDateFormatter *df = [[NSDateFormatter alloc] init];

    df.timeStyle = NSDateFormatterMediumStyle;
    df.dateStyle = NSDateFormatterShortStyle;
    df.doesRelativeDateFormatting = YES;
    NSLog(@"STRING DATEEE : %@ REAL DATE TODAY %@",[df stringFromDate:strDate],[NSDate date]);
      return [df stringFromDate:strDate];

}

I have date string with the following format "2013-10-29T09:38:00"

When I tried to give the NSDate object then its always return me null date.
so I tried to convert that date in to yyyy-MM-dd HH:mm:ssZZZZ then I pass this date to function then it's just printing whole date..

How to solve this problem?

//Following is the code I call the above function

NSDateFormatter *formatter = [[NSDateFormatter alloc] init];
[formatter setDateFormat:@"yyyy-MM-dd'T'HH:mm:ss"];
NSDate *date = [formatter dateFromString:[threadDict objectForKey:@"lastMessageDate"]];
[formatter setDateFormat:@"yyyy-MM-dd HH:mm:ssZZZZ"];

NSString *date1 = [formatter stringFromDate:date];
NSDate *date_d = [formatter dateFromString:date1];
NSString *resultstr=[UserManager getDateDiffrence:date];

self.dateLabel.text=resultstr;

回答1:

For simplicity I'm assuming that the dates you are formatting are all in the past (no "tomorrow" or "next week"). It's not that it can't be done but it would be more cases to deal with and more strings to return.

---

You can use components:fromDate:toDate:options: with whatever combination of date components you are looking for to get the number of years, months, weeks, days, hours, etc. between two dates. By then going though them in order from most significant (e.g. year) to least significant (e.g. day), you can format a string based only on the most significant component.

For example: a date that is 1 week, 2 days and 7 hours ago would be formatted as "1 week".

If you want to create special strings for a special number of a unit, like "tomorrow" for "1 day ago" then you can check the value of that component after you have determined that it is the most significant component.

The code would look something like this:

- (NSString *)relativeDateStringForDate:(NSDate *)date
{
    NSCalendarUnit units = NSCalendarUnitDay | NSCalendarUnitWeekOfYear | 
                           NSCalendarUnitMonth | NSCalendarUnitYear;

    // if `date` is before "now" (i.e. in the past) then the components will be positive
    NSDateComponents *components = [[NSCalendar currentCalendar] components:units
                                                                   fromDate:date
                                                                     toDate:[NSDate date]
                                                                    options:0];

    if (components.year > 0) {
        return [NSString stringWithFormat:@"%ld years ago", (long)components.year];
    } else if (components.month > 0) {
        return [NSString stringWithFormat:@"%ld months ago", (long)components.month];
    } else if (components.weekOfYear > 0) {
        return [NSString stringWithFormat:@"%ld weeks ago", (long)components.weekOfYear];
    } else if (components.day > 0) {
        if (components.day > 1) {
            return [NSString stringWithFormat:@"%ld days ago", (long)components.day];
        } else {
            return @"Yesterday";
        }
    } else {
        return @"Today";
    }
}

---

If your dates could also be in the future then you can check the absolute value of the components in the same order and then check if it's positive or negative to return the appropriate strings. I'me only showing the year below:

if ( abs(components.year > 0) ) { 
    // year is most significant component
    if (components.year > 0) {
        // in the past
        return [NSString stringWithFormat:@"%ld years ago", (long)components.year];
    } else {
        // in the future
        return [NSString stringWithFormat:@"In %ld years", (long)components.year];
    }
} 

回答2:

Swift update, thanks to objective-c answer of David Rönnqvist, it will work for the past dates.

func relativeDateStringForDate(date : NSDate) -> NSString {

        let todayDate = NSDate()
        let units: NSCalendarUnit = [.Hour, .Day, .Month, .Year, .WeekOfYear]
        let components = NSCalendar.currentCalendar().components(units, fromDate: date , toDate: todayDate, options: NSCalendarOptions.MatchFirst )

        let year =  components.year
        let month = components.month
        let day = components.day
        let hour = components.hour
        let weeks = components.weekOfYear
        // if `date` is before "now" (i.e. in the past) then the components will be positive

        if components.year > 0 {
            return NSString.init(format: "%d years ago", year);
        } else if components.month > 0 {
            return NSString.init(format: "%d months ago", month);
        } else if components.weekOfYear > 0 {
            return NSString.init(format: "%d weeks ago", weeks);
        } else if (components.day > 0) {
            if components.day > 1 {
                return NSString.init(format: "%d days ago", day);
            } else {
                return "Yesterday";
            }
        } else {
            return NSString.init(format: "%d hours ago", hour);
        }
    }

回答3:

FOR: SWIFT 3

Here's a Swift 3 version, for past dates, that handles all units and singular or plural in the returned String.

Example Use:

let oneWeekAgo = Calendar.current.date(byAdding: .weekOfYear, value: -1, to: Date())!

print(relativePast(for: oneWeekAgo)) // output: "1 week ago"

I based it on a riff off of Saurabh Yadav's. Thanks.

func relativePast(for date : Date) -> String {

    let units = Set<Calendar.Component>([.year, .month, .day, .hour, .minute, .second, .weekOfYear])
    let components = Calendar.current.dateComponents(units, from: date, to: Date())

    if components.year! > 0 {
        return "\(components.year!) " + (components.year! > 1 ? "years ago" : "year ago")

    } else if components.month! > 0 {
        return "\(components.month!) " + (components.month! > 1 ? "months ago" : "month ago")

    } else if components.weekOfYear! > 0 {
        return "\(components.weekOfYear!) " + (components.weekOfYear! > 1 ? "weeks ago" : "week ago")

    } else if (components.day! > 0) {
        return (components.day! > 1 ? "\(components.day!) days ago" : "Yesterday")

    } else if components.hour! > 0 {
        return "\(components.hour!) " + (components.hour! > 1 ? "hours ago" : "hour ago")

    } else if components.minute! > 0 {
        return "\(components.minute!) " + (components.minute! > 1 ? "minutes ago" : "minute ago")

    } else {
        return "\(components.second!) " + (components.second! > 1 ? "seconds ago" : "second ago")
    }
}

回答4:

Here's my answer (in Swift 3!) and why it's better.

Answer:

func datePhraseRelativeToToday(from date: Date) -> String {

    // Don't use the current date/time. Use the end of the current day 
    // (technically 0h00 the next day). Apple's calculation of 
    // doesRelativeDateFormatting niavely depends on this start date.
    guard let todayEnd = dateEndOfToday() else {
        return ""
    }

    let calendar = Calendar.autoupdatingCurrent

    let units = Set([Calendar.Component.year,
                 Calendar.Component.month,
                 Calendar.Component.weekOfMonth,
                 Calendar.Component.day])

    let difference = calendar.dateComponents(units, from: date, to: todayEnd)

    guard let year = difference.year,
        let month = difference.month,
        let week = difference.weekOfMonth,
        let day = difference.day else {
            return ""
    }

    let timeAgo = NSLocalizedString("%@ ago", comment: "x days ago")

    let dateFormatter: DateFormatter = {
        let formatter = DateFormatter()
        formatter.locale = Locale.autoupdatingCurrent
        formatter.dateStyle = .medium
        formatter.doesRelativeDateFormatting = true
        return formatter
    }()

    if year > 0 {
        // sample output: "Jan 23, 2014"
        return dateFormatter.string(from: date)
    } else if month > 0 {
        let formatter = DateComponentsFormatter()
        formatter.unitsStyle = .brief // sample output: "1mth"
        formatter.allowedUnits = .month
        guard let timePhrase = formatter.string(from: difference) else {
            return ""
        }
        return String(format: timeAgo, timePhrase)
    } else if week > 0 {
        let formatter = DateComponentsFormatter()
        formatter.unitsStyle = .brief; // sample output: "2wks"
        formatter.allowedUnits = .weekOfMonth
        guard let timePhrase = formatter.string(from: difference) else {
            return ""
        }
        return String(format: timeAgo, timePhrase)
    } else if day > 1 {
            let formatter = DateComponentsFormatter()
            formatter.unitsStyle = .abbreviated; // sample output: "3d"
            formatter.allowedUnits = .day
            guard let timePhrase = formatter.string(from: difference) else {
                return ""
            }
            return String(format: timeAgo, timePhrase)
    } else {
        // sample output: "Yesterday" or "Today"
        return dateFormatter.string(from: date)
    }
}

func dateEndOfToday() -> Date? {
    let calendar = Calendar.autoupdatingCurrent
    let now = Date()
    let todayStart = calendar.startOfDay(for: now)
    var components = DateComponents()
    components.day = 1
    let todayEnd = calendar.date(byAdding: components, to: todayStart)
    return todayEnd
}

Remember to reuse your formatters to avoid any performance hit! Hint: extensions on DateFormatter and DateComponentsFormatter are good ideas.

Why it's better:

• Utilizes DateFormatter's "Yesterday" and "Today". This is already translated by Apple, which saves you work!
• Uses DateComponentsFormatter's already translated "1 week" string. (Again less work for you, courtesy of Apple.) All you have to do is translate the "%@ ago" string.