iOS中日期有关方法小结

1、判断某一天是一年中的第几天

NSDateFormatter *formatter = [[NSDateFormatter
alloc]
init];
[formatter
setDateFormat:@"yyyy-MM-dd"];
NSDate *date = [formatter
dateFromString:@"2012-1-1"];

NSCalendar *gregorian = [NSCalendar
currentCalendar];
NSDateComponents *weekOfYearComponents = [gregorian
components:NSWeekOfYearCalendarUnit
fromDate:date];
NSInteger weekofyear = [weekOfYearComponents
weekOfYear];

NSLog(@"weekofyear number = %d" , weekofyear);