随笔-OC获取系统时间，获取绝对时间，获得真实时间

1. //获得系统时间
2. NSDate * senddate=[NSDate date];
3. NSDateFormatter *dateformatter=[[NSDateFormatter alloc] init];
4. [dateformatter setDateFormat:@"HH:mm"];
5. NSString * locationString=[dateformatter stringFromDate:senddate];
6. //[dateformatter setDateFormat:@"YYYY-MM-dd-HH-mm-ss"];
7. //NSString * morelocationString=[dateformatter stringFromDate:senddate];
8. 
   
9. //获得系统日期
10. NSCalendar * cal=[NSCalendar currentCalendar];
11. NSUInteger unitFlags=NSDayCalendarUnit|NSMonthCalendarUnit|NSYearCalendarUnit;
12. NSDateComponents * conponent= [cal components:unitFlags fromDate:senddate];
13. NSInteger year=[conponent year];
14. NSInteger month=[conponent month];
15. NSInteger day=[conponent day];
16. NSString * nsDateString= [NSString stringWithFormat:@"M年-月-日",year,month,day];
17. 
    
18. [dateformatter release];

2. 从字符串来获得NSDate

1. string strYear="1988";
2. string strMonth="09";
3. string strDay="18";
4. string strHour="5";
5. string strMinutes="18";
6. string strSec="20";
7. 
   
8. 
   
9. 
   
10. morelocationString=[NSString stringWithFormat:@"%s-%s-%s-%s-%s-%s",strYear.c_str(),strMonth.c_str(),
11. strDay.c_str(),strHour.c_str(),strMinutes.c_str(),strSec.c_str()];
12. 
    
13. 
    
14. //根据时间字符串获得NSDate
15. NSDateFormatter *dateformatter=[[NSDateFormatter alloc] init];
16. [dateformatter setDateFormat:@"YYYY-MM-dd-HH-mm-ss"];
17. NSDate * oldDate=[dateformatter dateFromString:morelocationString];

3. 从GMT时间，得到本地时间

1. NSDate * oldDate=[dateformatter dateFromString:morelocationString];
2. 
   
3. 
   
4. NSTimeInterval timeZoneOffset=[[NSTimeZone systemTimeZone] secondsFromGMT];
5. NSDate * newDate=[oldDate dateByAddingTimeInterval:timeZoneOffset];