Objective-c NSDate 取时间，日期，星期，毫秒等

NSDate

//得到当前的日期
 NSDate *date = [NSDate date];
 NSLog(@"date:%@",date);
 
 //得到(24 * 60 * 60)即24小时之前的日期，dateWithTimeIntervalSinceNow:
 NSDate *yesterday = [NSDate dateWithTimeIntervalSinceNow: -(24 * 60 * 60)];
 NSLog(@"yesterday:%@",yesterday);

NSDateFormatter *formatter =[[[NSDateFormatter alloc] init] autorelease];
 NSDate *date = [NSDate date];
 [formatter setTimeStyle:NSDateFormatterMediumStyle];
 NSCalendar *calendar = [[[NSCalendar alloc] initWithCalendarIdentifier:NSGregorianCalendar] autorelease];
 NSDateComponents *comps = [[[NSDateComponents alloc] init] autorelease];
 NSInteger unitFlags = NSYearCalendarUnit | 
                       NSMonthCalendarUnit |
                       NSDayCalendarUnit | 
                       NSWeekdayCalendarUnit | 
                       NSHourCalendarUnit |
                       NSMinuteCalendarUnit |
                       NSSecondCalendarUnit;
 //int week=0;
 comps = [calendar components:unitFlags fromDate:date];
 int week = [comps weekday]; 
 int year=[comps year]; 
 int month = [comps month];
 int day = [comps day];
 //[formatter setDateStyle:NSDateFormatterMediumStyle];
 //This sets the label with the updated time.
 int hour = [comps hour];
 int min = [comps minute];
 int sec = [comps second];
 NSLog(@"week%d",week);
 NSLog(@"year%d",year);
 NSLog(@"month%d",month);
 NSLog(@"day%d",day);
 NSLog(@"hour%d",hour);
 NSLog(@"min%d",min);
 NSLog(@"sec%d",sec);

 

//得到毫秒
NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
 [dateFormatter setDateStyle:NSDateFormatterMediumStyle];
 [dateFormatter setTimeStyle:NSDateFormatterShortStyle];
 //[dateFormatter setDateFormat:@"hh:mm:ss"]
 [dateFormatter setDateFormat:@"yyyy-MM-dd HH:mm:ss.SSS"];
 NSLog(@"Date%@", [dateFormatter stringFromDate:[NSDate date]]);
 [dateFormatter release];

iPhone NSDate 时间间隔

NSDate *beginTime = [NSDate date];
....
NSTimeInterval loadDuration = [beginTime timeIntervalSinceNow];

关于NSTimeInterval的使用

NSTimeInterval time = [[NSDate date] timeIntervalSince1970]; 可以这样定义 
NSLog(@"当前时间为%f", time);  打印出从1970年开始到现在的秒数. 

可见time可以赋值给float类型 
所以可以这样写： 
float a ＝ time； 

这样就可以很容易的到两个时间点中间相差多少秒。