iOS开发NSDate、NSString、时间戳之间的转化

 //将UTCDate(世界标准时间)转化为当地时区的标准Date（钟表显示的时间）
 //NSDate *date = [NSDate date];   2018-03-27 06:54:41 +0000
 //转化后：2018-03-27 14:54:41 +0000
 -(NSDate *)getLocalDateFromUTCDate:(NSDate *)UTCDate{

     NSTimeZone *tz = [NSTimeZone defaultTimeZone];
     NSInteger seconds = [tz secondsFromGMTForDate: UTCDate];
     return [NSDate dateWithTimeInterval: seconds sinceDate: UTCDate];

 }

 //将当地时区的标准Date转化为UTCDate
 //当前当地的标准时间：2018-03-27 14:54:41 +0000
 //转化为世界标准时间:2018-03-27 06:54:41 +0000
 -(NSDate *)getUTCDateFromLocalDate:(NSDate *)LocalDate{

     NSTimeZone *tz = [NSTimeZone defaultTimeZone];
     NSInteger seconds = -[tz secondsFromGMTForDate: LocalDate];
     return [NSDate dateWithTimeInterval: seconds sinceDate: LocalDate];

 }

 //根据UTCDate获取当前时间字符串（钟表上显示的时间）
 //输入：[NSDate date]     2018-03-27 07:44:05 +0000
 //输出：2018-03-27 15:44:05
 -(NSString *)localStringFromUTCDate:(NSDate *)UTCDate{

     NSDateFormatter *dateFormatter = [[NSDateFormatter alloc]init];
     NSTimeZone *tz = [NSTimeZone defaultTimeZone];
     [dateFormatter setTimeZone:tz];
     [dateFormatter setDateFormat:@"yyyy-MM-dd HH:mm:ss"];
     NSString* result=[dateFormatter stringFromDate:UTCDate];
     return result;

 }

 //根据UTC字符串获取当前时间字符串（钟表上显示的时间）
 //输入：2018-03-27 07:44:05
 //输出：2018-03-27 15:44:05
 -(NSString *)localStringFromUTCString:(NSString *)UTCString{

     //先将UTC字符串转为UTCDate;
     NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
     NSTimeZone *tz = [NSTimeZone timeZoneWithAbbreviation:@"GMT"];
     [dateFormatter setTimeZone:tz];
     [dateFormatter setDateFormat:@"yyyy-MM-dd HH:mm:ss"];
     NSDate *UTCDate = [dateFormatter dateFromString:UTCString];

     [dateFormatter setTimeZone:[NSTimeZone defaultTimeZone]];
     NSString* result = [dateFormatter stringFromDate:UTCDate];
     return result;
 }

 //将当前时间字符串转为UTCDate
 -(NSDate *)UTCDateFromLocalString:(NSString *)localString{

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

 //将当前时间字符串转为UTC字符串
 -(NSString *)UTCStringFromLocalString:(NSString *)localString{

     NSDate *date = [self UTCDateFromLocalString:localString];
     NSString *string = [NSString stringWithFormat:@"%@",date];
     NSString *result = [string substringToIndex:string.length-];
     return result;

 }

 //UTCDate转UTC字符串
 -(NSString *)UTCStringFromUTCDate:(NSDate *)UTCDate{

     NSDateFormatter *dataFormatter = [[NSDateFormatter alloc]init];
     [dataFormatter setDateFormat:@"yyyy-MM-dd HH:mm:ss"];
     NSTimeZone *tz = [NSTimeZone timeZoneWithAbbreviation:@"GMT"];
     [dataFormatter setTimeZone:tz];
     NSString *UTCString = [dataFormatter stringFromDate:UTCDate];
     return UTCString;

 }

 //将当前时间（UTCDate）转为时间戳
 -(NSString *)timeStampFromUTCDate:(NSDate *)UTCDate{

     NSTimeInterval timeInterval = [UTCDate timeIntervalSince1970];
     // *1000,是精确到毫秒；这里是精确到秒;
     NSString *result = [NSString stringWithFormat:@"%.0f",timeInterval];
     return result;

 }

 //当前时间字符串(钟表上显示的时间)转为时间戳
 -(NSString *)timeStamapFromLocalString:(NSString *)localString{

     //先转为UTCDate
     NSDate *UTCDate = [self UTCDateFromLocalString:localString];
     NSString *timeStamap = [self timeStampFromUTCDate:UTCDate];
     return timeStamap;

 }

 //将UTCString转为时间戳
 -(NSString *)timeStamapFromUTCString:(NSString *)UTCString{

     //先将UTC字符串转为UTCDate;
     NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
     NSTimeZone *tz = [NSTimeZone timeZoneWithAbbreviation:@"GMT"];
     [dateFormatter setTimeZone:tz];
     [dateFormatter setDateFormat:@"yyyy-MM-dd HH:mm:ss"];
     NSDate *UTCDate = [dateFormatter dateFromString:UTCString];

     NSString *timeStamap = [self timeStampFromUTCDate:UTCDate];
     return timeStamap;
 }

 //时间戳转UTCDate
 -(NSDate *)UTCDateFromTimeStamap:(NSString *)timeStamap{

     NSTimeInterval timeInterval=[timeStamap doubleValue];
     //  /1000;传入的时间戳timeStamap如果是精确到毫秒的记得要/1000
     NSDate *UTCDate=[NSDate dateWithTimeIntervalSince1970:timeInterval];
     return UTCDate;

 }

若是想要将时间戳转为字符串，可根据获得的UTCDate再进行转化