iOS：NSDate的主要几种时间形式

//获取当前日期
NSDate *date = sender.date;
NSLog(@"%@",date);

　　//date转字符串
NSDateFormatter *formatter = [[NSDateFormatter alloc]init];
//YYYY:年 MM:月 dd:日 HH：24小时制  hh：12小时制
formatter.dateFormat = @"YYYY-MM-dd HH:mm:ss";
NSString *strdate = [formatter stringFromDate:date];
NSLog(@"%@",strdate);

//字符串转date
NSDate *date2 = [formatter dateFromString:strdate];
NSLog(@"%@",date2);

//将日期分解为年月日
NSCalendar *calendar = [NSCalendar currentCalendar];
NSInteger unitflags = NSCalendarUnitYear | NSCalendarUnitMonth | NSCalendarUnitDay;
NSDateComponents *components = [calendar components:unitflags fromDate:date];
NSLog(@"year:%ld  month:%ld  day:%ld",[components year],[components month],[components day]);

//将年月日组合成日期
[components setYear:2014];
[components setMonth:9];
[components setDay:1];
NSDate *date3 = [calendar dateFromComponents:components];
NSLog(@"%@",date3);