title: NSCalendar NSDateComponents weekofYear return 1 with date 2014-12-31
body: <p>I want to get weekofYear with date '2014-12-31' ,but it always return 1 not 52 
  here is my code:</p>
  
  <pre><code>NSCalendar *calendar = [NSCalendar currentCalendar];
  NSUInteger unitFlags = NSYearCalendarUnit | NSMonthCalendarUnit | NSDayCalendarUnit | NSHourCalendarUnit | NSMinuteCalendarUnit | NSSecondCalendarUnit | NSWeekdayCalendarUnit | NSWeekOfMonthCalendarUnit | NSWeekOfYearCalendarUnit;
  NSDateComponents *dateComponent = [calendar components:unitFlags fromDate:[NSDate date]];
  
  NSlog(@"%i",dateComponent.weekOfYear);
  
  
  output  "1";
  </code></pre>
  
  <p>I know result is right, but I want get "52" not '1',how to fix it?</p>