IOS 时间和时间戳之间转化

以毫秒为整数值的时间戳转换

- (NSString *)timeWithTimeIntervalString:(NSString *)timeString
{
// 格式化时间
NSDateFormatter* formatter = [[NSDateFormatter alloc] init];
formatter.timeZone = [NSTimeZone timeZoneWithName:@"shanghai"];
[formatter setDateStyle:NSDateFormatterMediumStyle];
[formatter setTimeStyle:NSDateFormatterShortStyle];
[formatter setDateFormat:@"yyyy年MM月dd日 HH:mm"];

// 毫秒值转化为秒
NSDate* date = [NSDate dateWithTimeIntervalSince1970:[timeString doubleValue]/ 1000.0];
NSString* dateString = [formatter stringFromDate:date];
return dateString;
}

// 当前时间
NSDate* date = [NSDate dateWithTimeIntervalSinceNow:0];
NSTimeInterval a=[date timeIntervalSince1970]*1000; // *1000 是精确到毫秒，不乘就是精确到秒
NSString *timeString = [NSString stringWithFormat:@"%.0f", a]; //转为字符型

- (void)getBabyDetailAge:(NSString *)date
{
// 获得日期对象
NSDateFormatter *formatter_ = [[NSDateFormatter alloc] init];
formatter_.dateFormat = @"yyyy-MM-dd HH:mm:ss";
NSDate *createDate = [formatter_ dateFromString:date];

NSCalendar *gregorian = [[ NSCalendar alloc ] initWithCalendarIdentifier : NSCalendarIdentifierGregorian];
NSUInteger unitFlags = NSCalendarUnitDay | NSCalendarUnitMonth | NSCalendarUnitYear;
NSDateComponents *components = [gregorian components:unitFlags fromDate:createDate toDate:[NSDate date] options: 0 ];

NSInteger years = [components year];
NSInteger months = [components month ];
NSInteger days = [components day ];
}