iOS与日期相关的操作

// Do any additional setup after loading the view, typically from a nib.

    //得到当前的日期  注意week1是星期天

    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];

    //NSDate *date_ = [NSDate date];

    [formatter setTimeStyle:NSDateFormatterMediumStyle];

    NSCalendar *calendar = [[NSCalendar alloc] initWithCalendarIdentifier:NSGregorianCalendar];

    NSDateComponents *comps = [[NSDateComponents alloc] init];

    NSInteger unitFlags = NSYearCalendarUnit |

    NSMonthCalendarUnit |

    NSDayCalendarUnit |

    NSWeekdayCalendarUnit |

    NSHourCalendarUnit |

    NSMinuteCalendarUnit |

    NSSecondCalendarUnit;

    //int week=0;week1是星期天,week7是星期六;

    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,[self week: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]]);

-(NSString*)week:(NSInteger)week

{

    NSString*weekStr=nil;

    if(week==1)

    {

        weekStr=@"星期天";

    }else if(week==2){

        weekStr=@"星期一";

    }else if(week==3){

        weekStr=@"星期二";

    }else if(week==4){

        weekStr=@"星期三";

    }else if(week==5){

        weekStr=@"星期四";

    }else if(week==6){

        weekStr=@"星期五";

    }else if(week==7){

        weekStr=@"星期六";

    }

    return weekStr;

}

由NSDate
转换为NSString:

 NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];

[dateFormatter setDateFormat:@"yyyy-MM-dd HH:mm:ss"];

NSString *strDate = [dateFormatter stringFromDate:[NSDate date]];

NSLog(@"%@", strDate);

由NSString
转换为NSDate:

 NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];

[dateFormatter setDateFormat:@"yyyy-MM-dd HH:mm:ss"];

NSDate *date = [dateFormatter dateFromString:@"2010-08-04 16:01:03"];

NSLog(@"%@", date);