~日前表示

地味にハマったので残します。和暦に注意。

viewController.m

- (void)viewDidLoad {

    NSDateFormatter *formatter = [[NSDateFormatter alloc] init];
    [formatter setDateFormat:@"yyyy-MM-dd HH:mm:ss"];
    NSCalendar *calendar = [[NSCalendar alloc] initWithCalendarIdentifier:NSGregorianCalendar];
    [formatter setCalendar:calendar];
    NSDate *date = [formatter dateFromString:@"2015-02-04 00:00:00"];

    UILabel *label = [UILabel alloc]init];
    label.text = [self displayDate:date];

}

- (NSString *)displayDate:(NSDate*)timestamp {

    NSDate *now = [NSDate date];
    NSTimeInterval passed = [now timeIntervalSinceDate:timestamp];
    int min = passed / 60;
    if (min <= 1) {
        return @"1分前";
    }
    if (min < 60) {
        return [NSString stringWithFormat:@"%d分前", min];
    }
    int hour = min / 60;
    if (hour < 24) {
        return [NSString stringWithFormat:@"%d時間前", hour];
    }
    int day = hour / 24;
    return [NSString stringWithFormat:@"%d日前", day];
}