Accessing specific child elements when parsing RSS

Question

Dear Scholars I am trying to parse a RSS feed with the following item element structure

<item> 
         <title>Title</title> 
         <link>http://somelink.com</link> 
         <description>The description</description> 
         <author>[e-mail]</author> 
         <guid isPermaLink="false">http://youtube.com/?v=XBE4AX0Iuvw</guid> 
         <pubDate>Thu, 11 Nov 2010 10:56:44 +0000</pubDate> 
         <media:title>Media Title</media:title> 
         <media:thumbnail width="120" url="http://i1.ytimg.com/vi/XBE4AX0Iuvw/default.jpg" height="90"/> 
         <media:category label="Tags"/> 
         <media:player url="http://youtube.com/?v=XBE4AX0Iuvw"/> 
         <media:credit>Credit name</media:credit> 
         <enclosure url="http://youtube.com/v/XBE4AX0Iuvw.swf" duration="104" type="application/x-shockwave-flash"/> 
</item> 

Please note the tag media:thumbnail.url of which my question is related to.

Parser code:

// string contants found in the RSS feed
static NSString *kIDStr     = @"link";
static NSString *kNameStr   = @"thumbnail";
static NSString *kImageStr  = @"media:thumbnail";
static NSString *kArtistStr = @"description";
static NSString *kEntryStr  = @"item";


- (void)parser:(NSXMLParser *)parser didStartElement:(NSString *)elementName
                                            namespaceURI:(NSString *)namespaceURI
                                           qualifiedName:(NSString *)qName
                                              attributes:(NSDictionary *)attributeDict
    {
        // entry: { id (link), im:name (app name), im:image (variable height) }
        //
        NSLog(@"%@",elementName); 
        // I can see all top level elements,even media:thumbnail

        if ([elementName isEqualToString:kEntryStr])
        {
            self.workingEntry = [[[AppRecord alloc] init] autorelease];
        }
        storingCharacterData = [elementsToParse containsObject:elementName];
    }

    - (void)parser:(NSXMLParser *)parser didEndElement:(NSString *)elementName
                                          namespaceURI:(NSString *)namespaceURI
                                         qualifiedName:(NSString *)qName
    {
        if (self.workingEntry)
        {
            if (storingCharacterData)
            {


        NSString *trimmedString = [workingPropertyString stringByTrimmingCharactersInSet:
                                           [NSCharacterSet whitespaceAndNewlineCharacterSet]];

                [workingPropertyString setString:@""];  // clear the string for next time

                if ([elementName isEqualToString:kIDStr])
                {
                    self.workingEntry.appURLString = trimmedString;
                }
                else if ([elementName isEqualToString:kNameStr])
                {        
                    self.workingEntry.appName = trimmedString;
                }
                else if ([elementName isEqualToString:kImageStr])
                {

NSLog(@"The Content: %@",workingPropertyString); // Comes back empty, I guess due to the fact it has children inside.               


// QUESTION: How do I get the value stored in media:thumbnail   .url  
//NSLog(@">>>>>>>>>>>>> %@ / %@",[elementsToParse objectAtIndex:2],workingPropertyString);



                self.workingEntry.imageURLString = trimmedString;
                }
                else if ([elementName isEqualToString:kArtistStr])
                {
                    self.workingEntry.artist = trimmedString;

                }
            }
            else if ([elementName isEqualToString:kEntryStr])
            {
                [self.workingArray addObject:self.workingEntry];  
                self.workingEntry = nil;
            }
        }

    }

It seems to be a matter of syntax which I am not familiar with, which grabs the value stored in media:thumbnail.url. Can someone be as kind as to assist me in how do do so?

Answer 1

As url is an attribute of the media:thumbnail element, you need to access it via the attributes dictionary in didStartElement:. The foundCharacters: message (which I assume is where you're accumulating text into workingPropertyString) is only sent for character data between an element's start and end tags.

Answer 2

Hii Friends,

 i have similiar issue of retriving image url from MediaThumbnail attr from my feed,

you can write this at didStartElement as it check media:thumnail inside url where we can fetch image url String ,and it works for me

  if ([elementName isEqualToString:kEntryStr])
{
    self.workingEntry = [[[AppRecord alloc] init] autorelease];
}
else if([elementName isEqualToString:@"media:thumbnail"]) {
NSMutableString *currentImgUrl = [[NSMutableString alloc] init];
    [currentImgUrl appendString:[attributeDict objectForKey:@"url"]];
    NSLog(@"url:%@",currentImgUrl);
    self.workingEntry.imageURLString = currentImgUrl;
}
storingCharacterData = [elementsToParse containsObject:elementName];

Answer 3

To get a media:thumbnail (or and any element value) in a xml file easily,
use xpath query. In order to do XPathQuery you can use libxml2

Your XPath Query will sound like that : //media:thumbnail/@url
and will give you : http://i1.ytimg.com/vi/XBE4AX0Iuvw/default.jpg

read this : Using libxml2 for XML parsing and XPath queries in Cocoa (folow the instructions)