IOS-NSDate之今天，昨天，这周，这个月，上个月

今天跟大家讨论日期的用法，相信大家在项目中，经常会设置一个默认时间段，比如一周前到今天。下面教大家怎么获取前一天，或前一周等等。

比如date 2009-12-11

NSDate *today = [NSDate dateWithString:@"2009-12-11 00:00:00 +0000"]; NSDate *yesterday = [NSDate dateWithString:@"2009-12-10 00:00:00 +0000"]; NSDate *thisWeek = [NSDate dateWithString:@"2009-12-06 00:00:00 +0000"]; NSDate *lastWeek = [NSDate dateWithString:@"2009-11-30 00:00:00 +0000"]; NSDate *thisMonth = [NSDate dateWithString:@"2009-12-01 00:00:00 +0000"]; NSDate *lastMonth = [NSDate dateWithString:@"2009-11-01 00:00:00 +0000"];要求出上面的时间NSCalendar *cal = [NSCalendar currentCalendar];NSDateComponents *components = [cal components:( NSHourCalendarUnit | NSMinuteCalendarUnit | NSSecondCalendarUnit ) fromDate:[[NSDate alloc] init]];[components setHour:-[components hour]];[components setMinute:-[components minute]];[components setSecond:-[components second]];NSDate *today = [cal dateByAddingComponents:components toDate:[[NSDate alloc] init] options:0]; //This variable should now be pointing at a date object that is the start of today (midnight);[components setHour:-24];[components setMinute:0];[components setSecond:0];NSDate *yesterday = [cal dateByAddingComponents:components toDate: today options:0];components = [cal components:NSWeekdayCalendarUnit | NSYearCalendarUnit | NSMonthCalendarUnit | NSDayCalendarUnit fromDate:[[NSDate alloc] init]];[components setDay:([components day] - ([components weekday] - 1))]; NSDate *thisWeek  = [cal dateFromComponents:components];[components setDay:([components day] - 7)];NSDate *lastWeek  = [cal dateFromComponents:components];[components setDay:([components day] - ([components day] -1))]; NSDate *thisMonth = [cal dateFromComponents:components];[components setMonth:([components month] - 1)]; NSDate *lastMonth = [cal dateFromComponents:components];NSLog(@"today=%@",today);NSLog(@"yesterday=%@",yesterday);NSLog(@"thisWeek=%@",thisWeek);NSLog(@"lastWeek=%@",lastWeek);NSLog(@"thisMonth=%@",thisMonth);NSLog(@"lastMonth=%@",lastMonth);