NSDate 哪些事

.什么是时间戳?

时间戳是自 1970 年 1 月 1 日（00:00:00 GMT）至当前时间的总秒数。

2.NSDate,时间戳,NSString 之间的转换

//string 转 date
+ (NSDate *)dateWithString:(NSString *)str dateFormater:(NSString *)dateFormat{

NSDateFormatter * formatter = [[NSDateFormatter alloc] init];
[formatter setDateFormat:dateFormat]; // 年-月-日 时:分:秒如@"yyyy-MM-dd hh:mm:ss"
NSDate * date = [formatter dateFromString:str];
return date;
}
//date 转 string
+ (NSString *)stringWithDate:(NSDate *)date dateFormater:(NSString *)dateFormat{

NSDateFormatter *formatter = [[NSDateFormatter alloc] init];
[formatter setDateFormat:dateFormat];
NSString *str = [formatter stringFromDate:date];
return str;

}
//字符串转时间戳
+(NSTimeInterval)dateStrToInterval:(NSString *)dateStr dateFormater:(NSString *)dateFormat{
NSDateFormatter *fo = [[NSDateFormatter alloc] init];
[fo setDateFormat:dateFormat];

NSDate *da = [fo dateFromString:dateStr];

if( da == nil )
return 0;

return da.timeIntervalSince1970;
}

//时间戳转字符串
+(NSString*)dateIntervalToString:(NSTimeInterval)timeInterval dateFormater:(NSString *)dateFormat{
if( !dateFormat )
return nil;
NSDateFormatter *fo = [[NSDateFormatter alloc] init];
[fo setDateFormat:dateFormat];

NSDate *da = [NSDate dateWithTimeIntervalSinceNow:(timeInterval+28800)/1000];
// [fo setDateStyle:kCFDateFormatterNoStyle];
NSString *daStr = [fo stringFromDate:da];
return daStr;
}

3.增加天数

NSDate * date = [NSDate date];

//明天
NSDate *afterToday = [date dateByAddingTimeInterval:60*60*24];

//昨天
NSDate *yesterday = [date dateByAddingTimeInterval: -60*60*24 ];

4.NSDate比较

 if (!([[NSDate date] timeIntervalSinceDate:[[NSDate date] dateByAddingTimeInterval:60*60*24]]]<60))

//多余的天数

  NSInteger num = [NSNumber numberWithDouble:[_currentOutDate timeIntervalSinceDate:_currentInDate]/3600/24].integerValue;

    self.accommodationL.text = [NSString stringWithFormat:@"住%ld晚",num]