获取发布时间距离当前时间的时间

- (NSDate *)dateFromString:(NSString *)dateString{

NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
[dateFormatter setDateFormat: @"yyyy-MM-dd HH:mm:ss"];
NSDate *destDate= [dateFormatter dateFromString:dateString];
return destDate;
}

- (NSString *)prettyDateWithReference:(NSDate *)reference {
NSString *suffix = @"ago";

NSDateFormatter *formatter = [[NSDateFormatter alloc] init];
formatter.dateFormat = @"yyyy-MM-dd HH:mm:ss";//日期格式
//   formatter.timeZone = [NSTimeZone systemTimeZone];//给定系统所在的时区
NSString *dateS = [formatter stringFromDate:[NSDate date]];
NSDate *date = [self dateFromString:dateS];
NSLog(@"%@",date);
NSLog(@"%@",dateS);

float different = [reference timeIntervalSinceDate:date];
if (different < 0) {
different = -different;
suffix = @"发布";
}

// days = different / (24 * 60 * 60), take the floor value
float dayDifferent = floor(different / 86400);

int days   = (int)dayDifferent;
int weeks  = (int)ceil(dayDifferent / 7);
int months = (int)ceil(dayDifferent / 30);
int years  = (int)ceil(dayDifferent / 365);

// It belongs to today
if (dayDifferent <= 0) {
// lower than 60 seconds
if (different < 60) {
return @"刚才";
}

// lower than 120 seconds => one minute and lower than 60 seconds
if (different < 120) {
return [NSString stringWithFormat:@"1分钟前 %@", suffix];
}

// lower than 60 minutes
if (different < 660 * 60) {
return [NSString stringWithFormat:@"%d 分钟前 %@", (int)floor(different / 60), suffix];
}

// lower than 60 * 2 minutes => one hour and lower than 60 minutes
if (different < 7200) {
return [NSString stringWithFormat:@"1小时前 %@", suffix];
}

// lower than one day
if (different < 86400) {
return [NSString stringWithFormat:@"%d 小时前 %@", (int)floor(different / 3600), suffix];
}
}
// lower than one week
else if (days < 7) {
return [NSString stringWithFormat:@"%d 天%@ %@", days, days == 1 ? @"" : @"s", suffix];
}
// lager than one week but lower than a month
else if (weeks < 4) {
return [NSString stringWithFormat:@"%d 星期%@ %@", weeks, weeks == 1 ? @"" : @"s", suffix];
}
// lager than a month and lower than a year
else if (months < 12) {
return [NSString stringWithFormat:@"%d 月%@ %@", months, months == 1 ? @"" : @"s", suffix];
}
// lager than a year
else {
return [NSString stringWithFormat:@"%d 年%@ %@", years, years == 1 ? @"" : @"s", suffix];
}

return self.description;
}