Classes/ParseOperation.m

/*
     File: ParseOperation.m 
 Abstract: NSOperation subclass for parsing the RSS feed.
  
  Version: 1.5 
  
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 */
 
#import "ParseOperation.h"
#import "AppRecord.h"
 
// string contants found in the RSS feed
static NSString *kIDStr     = @"id";
static NSString *kNameStr   = @"im:name";
static NSString *kImageStr  = @"im:image";
static NSString *kArtistStr = @"im:artist";
static NSString *kEntryStr  = @"entry";
 
 
@interface ParseOperation () <NSXMLParserDelegate>
 
// Redeclare appRecordList so we can modify it within this class
@property (nonatomic, strong) NSArray *appRecordList;
 
@property (nonatomic, strong) NSData *dataToParse;
@property (nonatomic, strong) NSMutableArray *workingArray;
@property (nonatomic, strong) AppRecord *workingEntry;  // the current app record or XML entry being parsed
@property (nonatomic, strong) NSMutableString *workingPropertyString;
@property (nonatomic, strong) NSArray *elementsToParse;
@property (nonatomic, readwrite) BOOL storingCharacterData;
 
@end
 
 
#pragma mark -
 
@implementation ParseOperation
 
// -------------------------------------------------------------------------------
//  initWithData:
// -------------------------------------------------------------------------------
- (instancetype)initWithData:(NSData *)data
{
    self = [super init];
    if (self != nil)
    {
        _dataToParse = data;
        _elementsToParse = @[kIDStr, kNameStr, kImageStr, kArtistStr];
    }
    return self;
}
 
// -------------------------------------------------------------------------------
//  main
//  Entry point for the operation.
//  Given data to parse, use NSXMLParser and process all the top paid apps.
// -------------------------------------------------------------------------------
- (void)main
{
    // The default implemetation of the -start method sets up an autorelease pool
    // just before invoking -main however it does NOT setup an excption handler
    // before invoking -main.  If an exception is thrown here, the app will be
    // terminated.
    
    _workingArray = [NSMutableArray array];
    _workingPropertyString = [NSMutableString string];
    
    // It's also possible to have NSXMLParser download the data, by passing it a URL, but this is not
    // desirable because it gives less control over the network, particularly in responding to
    // connection errors.
    //
    NSXMLParser *parser = [[NSXMLParser alloc] initWithData:self.dataToParse];
    [parser setDelegate:self];
    [parser parse];
    
    if (![self isCancelled])
    {
        // Set appRecordList to the result of our parsing
        self.appRecordList = [NSArray arrayWithArray:self.workingArray];
    }
    
    self.workingArray = nil;
    self.workingPropertyString = nil;
    self.dataToParse = nil;
}
 
 
#pragma mark - RSS processing
 
// -------------------------------------------------------------------------------
//  parser:didStartElement:namespaceURI:qualifiedName:attributes:
// -------------------------------------------------------------------------------
- (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) }
    //
    if ([elementName isEqualToString:kEntryStr])
    {
        self.workingEntry = [[AppRecord alloc] init];
    }
    self.storingCharacterData = [self.elementsToParse containsObject:elementName];
}
 
// -------------------------------------------------------------------------------
//  parser:didEndElement:namespaceURI:qualifiedName:
// -------------------------------------------------------------------------------
- (void)parser:(NSXMLParser *)parser didEndElement:(NSString *)elementName
                                      namespaceURI:(NSString *)namespaceURI
                                     qualifiedName:(NSString *)qName
{
    if (self.workingEntry != nil)
    {
        if (self.storingCharacterData)
        {
            NSString *trimmedString = [self.workingPropertyString stringByTrimmingCharactersInSet:
                                       [NSCharacterSet whitespaceAndNewlineCharacterSet]];
            [self.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])
            {
                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;
        }
    }
}
 
// -------------------------------------------------------------------------------
//  parser:foundCharacters:
// -------------------------------------------------------------------------------
- (void)parser:(NSXMLParser *)parser foundCharacters:(NSString *)string
{
    if (self.storingCharacterData)
    {
        [self.workingPropertyString appendString:string];
    }
}
 
// -------------------------------------------------------------------------------
//  parser:parseErrorOccurred:
// -------------------------------------------------------------------------------
- (void)parser:(NSXMLParser *)parser parseErrorOccurred:(NSError *)parseError
{
    if (self.errorHandler)
    {
        self.errorHandler(parseError);
    }
}
 
@end