NSDate NSDateFormatter NSTimeZone NSDateComponents NSCalendar

--------------------------------------------------------------------------NSDate----------------------------------------------------------------------------

NSDate:用来获取系统运行时时间.

1:获取IOS当前的运行时间

这样获取的是:世界标准时(UTC) 比中国时间晚8个小时

NSDate *date = [NSDate date];

2:为NSDate增加减少时间

NSDate *date = [[NSDate alloc] init];
NSTimeInterval time = 5;//单位为秒
NSLog(@"%@",date);
NSDate *newDate = [date dateByAddingTimeInterval:time];//加时间
//NSDate *newDate = [date dateByAddingTimeInterval:-time];//减时间
NSLog(@"%@",newDate);

注:遍历以往或者未来的天数可以通过 增加或减少时间来实现

3:比较时间是否相等

- (BOOL)isEqualToDate:(NSDate *)otherDate;//与otherDate比较，相同返回YES

 - (NSDate *)earlierDate:(NSDate *)anotherDate;

 - (NSDate *)laterDate:(NSDate *)anotherDate;

[endTime timeIntervalSinceDate:beginTime];

--------------------------------------------------------------------------NSDate----------------------------------------------------------------------------

-----------------------------------------------------------------NSDateFormatter------------------------------------------------------------------------

1:NSDate 转换成 NSString 格式的日期

NSDateFormatter * formatter =   [[NSDateFormatter alloc] init];
[formatter setDateFormat:@"yyyy-MM-dd HH:mm:ss"];
NSString *loctime = [formatter stringFromDate:date];
[formatter release]

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);
[dateFormatter release];

-----------------------------------------------------------------NSDateFormatter------------------------------------------------------------------------

-----------------------------------------------------------------NSDateComponents------------------------------------------------------------------------

NSDateComponents 是通过 NSCalendar 实例化的

1:通过NSDate获取 NSDateComponents

NSDateComponents *pastDateComponents = [[NSCalendar currentCalendar] components:NSYearCalendarUnit|NSMonthCalendarUnit|NSDayCalendarUnit|NSWeekdayCalendarUnit fromDate:pastDate];

-----------------------------------------------------------------NSDateComponents------------------------------------------------------------------------