CocoaXMLParser.m

/*
     File: CocoaXMLParser.m
 Abstract: Subclass of ShowRSSParser that uses the Foundation framework's NSXMLParser for parsing the XML data.
  Version: 1.3
 
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*/

#import "CocoaXMLParser.h"
#import "Show.h"

@implementation CocoaXMLParser

+ (NSString *)parserName {
    return @"NSXMLParser";
}

+ (XMLParserType)parserType {
    return XMLParserTypeNSXMLParser;
}

@synthesize currentString, currentShow, parseFormatter, xmlData, rssConnection, downloadAndParsePool;

- (void)downloadAndParse:(NSURL *)url {
    self.downloadAndParsePool = [[NSAutoreleasePool alloc] init];
    done = NO;
    self.parseFormatter = [[[NSDateFormatter alloc] init] autorelease];
    [parseFormatter setDateStyle:NSDateFormatterLongStyle];
    [parseFormatter setTimeStyle:NSDateFormatterNoStyle];
    // necessary because iTunes RSS feed is not localized, so if the device region has been set to other than US
    // the date formatter must be set to US locale in order to parse the dates
    [parseFormatter setLocale:[[[NSLocale alloc] initWithLocaleIdentifier:@"US"] autorelease]];
    self.xmlData = [NSMutableData data];
    [[NSURLCache sharedURLCache] removeAllCachedResponses];
    NSURLRequest *theRequest = [NSURLRequest requestWithURL:url];
    // create the connection with the request and start loading the data
    rssConnection = [[NSURLConnection alloc] initWithRequest:theRequest delegate:self];
    [self performSelectorOnMainThread:@selector(downloadStarted) withObject:nil waitUntilDone:NO];
    if (rssConnection != nil) {
        do {
            
            [[NSRunLoop currentRunLoop] runMode:NSDefaultRunLoopMode beforeDate:[NSDate distantFuture]];
        } while (!done);
    }
    self.rssConnection = nil;
    self.parseFormatter = nil;
    self.currentShow = nil;
    [downloadAndParsePool release];
    self.downloadAndParsePool = nil;
}

#pragma mark NSURLConnection Delegate methods

/*
 Disable caching so that each time we run this app we are starting with a clean slate. You may not want to do this in your application.
 */
- (NSCachedURLResponse *)connection:(NSURLConnection *)connection willCacheResponse:(NSCachedURLResponse *)cachedResponse {
    return nil;
}

// Forward errors to the delegate.
- (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error {
    done = YES;
    [self performSelectorOnMainThread:@selector(parseError:) withObject:error waitUntilDone:NO];
}

// Called when a chunk of data has been downloaded.
- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data {
    // Append the downloaded chunk of data.
    [xmlData appendData:data];
}

- (void)connectionDidFinishLoading:(NSURLConnection *)connection {
    [self performSelectorOnMainThread:@selector(downloadEnded) withObject:nil waitUntilDone:NO];
    NSXMLParser *parser = [[NSXMLParser alloc] initWithData:xmlData];
    parser.delegate = self;
    self.currentString = [NSMutableString string];
    NSTimeInterval start = [NSDate timeIntervalSinceReferenceDate];
    [parser parse];
    NSTimeInterval duration = [NSDate timeIntervalSinceReferenceDate] - start;
    [self performSelectorOnMainThread:@selector(addToParseDuration:) withObject:[NSNumber numberWithDouble:duration] waitUntilDone:NO];
    [self performSelectorOnMainThread:@selector(parseEnded) withObject:nil waitUntilDone:NO];
    [parser release];
    self.currentString = nil;
    self.xmlData = nil;
    // Set the condition which ends the run loop.
    done = YES; 
}

#pragma mark Parsing support methods

static const NSUInteger kAutoreleasePoolPurgeFrequency = 100;

- (void)finishedCurrentShow {
    [self performSelectorOnMainThread:@selector(parsedShow:) withObject:currentShow waitUntilDone:NO];
    // performSelectorOnMainThread: will retain the object until the selector has been performed
    // setting the local reference to nil ensures that the local reference will be released
    self.currentShow = nil;
    countOfParsedShows++;
    // Periodically purge the autorelease pool. The frequency of this action may need to be tuned according to the 
    // size of the objects being parsed. The goal is to keep the autorelease pool from growing too large, but 
    // taking this action too frequently would be wasteful and reduce performance.
    if (countOfParsedShows == kAutoreleasePoolPurgeFrequency) {
        [downloadAndParsePool release];
        self.downloadAndParsePool = [[NSAutoreleasePool alloc] init];
        countOfParsedShows = 0;
    }
}

#pragma mark NSXMLParser Parsing Callbacks

// Constants for the XML element names that will be considered during the parse. 
// Declaring these as static constants reduces the number of objects created during the run
// and is less prone to programmer error.
static NSString *kName_Item = @"item";
static NSString *kName_Title = @"title";
static NSString *kName_StartTime = @"startTime";
static NSString *kName_EndTime = @"endTime";
static NSString *kName_DayOfTheWeek = @"dayOfTheWeek";


- (void)parser:(NSXMLParser *)parser didStartElement:(NSString *)elementName namespaceURI:(NSString *)namespaceURI qualifiedName:(NSString *) qualifiedName attributes:(NSDictionary *)attributeDict {
    if ([elementName isEqualToString:kName_Item]) {
        self.currentShow = [[[Show alloc] init] autorelease];
    } else if ([elementName isEqualToString:kName_Title] || [elementName isEqualToString:kName_StartTime] || [elementName isEqualToString:kName_EndTime] || [elementName isEqualToString:kName_DayOfTheWeek]) {
        [currentString setString:@""];
        storingCharacters = YES;
    }
}

- (void)parser:(NSXMLParser *)parser didEndElement:(NSString *)elementName namespaceURI:(NSString *)namespaceURI qualifiedName:(NSString *)qName {
    if ([elementName isEqualToString:kName_Item]) {
        [self finishedCurrentShow];
    } else if ([elementName isEqualToString:kName_Title]) {
        currentShow.name = currentString;
    } else if ([elementName isEqualToString:kName_StartTime]) {
        currentShow.startTime = currentString;
    } else if ([elementName isEqualToString:kName_EndTime]) {
        currentShow.endTime = currentString;
    } else if ([elementName isEqualToString:kName_DayOfTheWeek]) {
        currentShow.dayOfTheWeek = currentString;
    } 
    storingCharacters = NO;
}


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

/*
 A production application should include robust error handling as part of its parsing implementation.
 The specifics of how errors are handled depends on the application.
 */
- (void)parser:(NSXMLParser *)parser parseErrorOccurred:(NSError *)parseError {
    // Handle errors as appropriate for your application.
}


@end