Sorting by date format in iphone

I am new to iph开发者_JS百科one development.I am sorting a mutable array with respect to date.But it is sorting Using the date parameter consider it as string.I want to sort it by date.How can i achieve that .Please help me out.

 NSSortDescriptor *descriptor = [[NSSortDescriptor alloc] initWithKey:@"pubDate" ascending:YES];
[stories sortUsingDescriptors:[NSArray arrayWithObjects:descriptor,nil]];

Can i use selectors? if so how should i use it?.Thanks.

-(void)parser:(NSXMLParser *)parser foundCharacters:(NSString *)string
{ 
    [dateString appendString:string];
}    

-(void)parser:(NSXMLParser *)parser didEndElement:(NSString *)elementName namespaceURI:(NSString *)namespaceURI qualifiedName:(NSString *)qName{  
  NSDateFormatter *df = [[[NSDateFormatter alloc] init]autorelease];
  [df setDateFormat:@"dd.MM.yyyy"]; //change the format if you are using it in different way
  NSDate *myDate = [df dateFromString: dateString];
  [dateArray addObject:myDate];
}

after that you can sort the array just using the way you wrote in question.

Is the pubDate property of the objects in your array NSStrings or NSDates? I use that exact code on an array of objects with NSDates and it works perfectly fine. If you're using NSStrings you'll want to first convert them to date objects so you can properly sort by date.