NSDateFormatter时区问题

使用NSDateFormatter转换时间字符串时，默认的时区是系统时区，如我们使用一般都是北京时间(＋8)，

如果直接使用

 [dateFormatter dateFromString:@"2012-01-01 00:00:00"];

你会发现实际转换为2011－12－31 16：00：00,少了8小时

所以我们要先指定时区为GMT再转换，如下：

 static NSString *GLOBAL_TIMEFORMAT = @"yyyy-MM-dd HH:mm:ss";
 static NSString *GLOBAL_TIMEBASE = @"2012-01-01 00:00:00";

     NSTimeZone* localzone = [NSTimeZone localTimeZone];
     NSTimeZone* GTMzone = [NSTimeZone timeZoneForSecondsFromGMT:0];
     NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
     [dateFormatter setDateFormat:GLOBAL_TIMEFORMAT];
     [dateFormatter setTimeZone:GTMzone];
     NSDate *bdate = [dateFormatter dateFromString:GLOBAL_TIMEBASE];

     NSDate *day = [NSDate dateWithTimeInterval:3600 sinceDate:bdate];

     [dateFormatter setTimeZone:localzone];
     NSLog(@"CurrentTime = %@", [dateFormatter stringFromDate:day]);

还可以如下：

 NSTimeZone* localzone = [NSTimeZone localTimeZone];
 NSTimeZone* GTMzone = [NSTimeZone timeZoneForSecondsFromGMT:0];
 NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
 [dateFormatter setDateFormat:GLOBAL_TIMEFORMAT];
 [dateFormatter setTimeZone:GTMzone];
 NSDate *bdate = [dateFormatter dateFromString:GLOBAL_TIMEBASE];
 NSDate *day = [NSDate dateWithTimeInterval:(3600 + [localzone secondsFromGMT]) sinceDate:bdate];
 NSString *text = [dateFormatter stringFromDate:day];