Simple and concise desktop Cocoa NSXMLParser example?

Question

I would like to look through the elements of a file and when one specific element comes out, output the contents in between the tag.

I tried to follow the example in the

Answer 1

If you click the "Next" link on that page and go onto "Handling XML Elements and Attributes" it will give you an example of how to code the delegates.

Apple provides a Mac example in ImageMap.

There's no difference between NSXMLParser on Mac and iPhone, so reading an iPhone example shouldn't be a problem.

Answer 2

This is based on something I originally wrote for Cut out a part of a long NSString. I copied the NSXMLParserDelegate code from that iOS project into an OS X project. It gets the text from a specific object in a web page.

.h file:

@interface so7576593AppDelegate : NSObject <NSApplicationDelegate, NSXMLParserDelegate> {
    NSWindow *window;
    IBOutlet NSTextField *textField;

    NSMutableString *divCharacters;
    BOOL captureCharacters; 
}

@property (assign) IBOutlet NSWindow *window;

@end

.m file:

#import "so7576593AppDelegate.h"

@implementation so7576593AppDelegate

@synthesize window;

- (void)applicationDidFinishLaunching:(NSNotification *)aNotification {
    captureCharacters = NO;
    NSURL *theURL = [NSURL URLWithString:@"http://maxnerios.yolasite.com/"];
    NSXMLParser *parser = [[NSXMLParser alloc] initWithContentsOfURL:theURL];
    [parser setDelegate:self];
    [parser parse];
    [parser release];

}

- (void)parser:(NSXMLParser *)parser didStartElement:(NSString *)elementName namespaceURI:(NSString *)namespaceURI qualifiedName:(NSString *)qualifiedName attributes:(NSDictionary *)attributeDict {
    if ([elementName isEqual:@"div"] && [[attributeDict objectForKey:@"id"] isEqual:@"I3_sys_txt"]) {
        captureCharacters = YES;
        divCharacters = [[NSMutableString alloc] initWithCapacity:500];
    }
}

- (void)parser:(NSXMLParser *)parser foundCharacters:(NSString *)string {
    if (captureCharacters) {
        //from parser:foundCharacters: docs:
        //The parser object may send the delegate several parser:foundCharacters: messages to report the characters of an element. 
        //Because string may be only part of the total character content for the current element, you should append it to the current 
        //accumulation of characters until the element changes.
        [divCharacters appendString:string];
    }
}

- (void)parser:(NSXMLParser *)parser didEndElement:(NSString *)elementName namespaceURI:(NSString *)namespaceURI qualifiedName:(NSString *)qName {
    if (captureCharacters) {
        captureCharacters = NO;
        [textField setStringValue:divCharacters];
        [divCharacters release];
    }
}

@end 

Answer 3

Here is an example of using an NSXMLParser in a custom class that takes in a string of the tag to look for and the xml NSData:

JHXMLParser.h:

@protocol JHXMLParserDelegate <NSObject>
@optional
- (void)acceptParsedData:(NSMutableArray *)parsedData withIdent:(NSString *)ident;
- (void)acceptParsedDebugData:(NSMutableArray *)parsedData withIdent:(NSString *)ident;

@end

@class JHKeyValuePair;

@interface JHXMLParser : NSObject <NSXMLParserDelegate> {
    NSString *ident;

    @private
    id _delegate;
    NSMutableArray *_parsedData;
    NSString *_key;
    NSData *_rawData;
    NSXMLParser *_dataParser;
    NSString *_previousTag;
    NSString *_currentTag;
}

@property (retain, nonatomic) NSString *ident;

- (id)initWithKeyValuePair:(JHKeyValuePair *)kvPair;
- (id)initWithKey:(NSString *)Key andData:(NSData *)data;
// delegate management. The delegate is not retained.
- (id <JHXMLParserDelegate>)delegate;
- (void)setDelegate:(id <JHXMLParserDelegate>)delegate;
- (BOOL)start;

@end

And the JHXMLParser.m:

#import "JHKeyValuePair.h"
#import "JHXMLParser.h"

@implementation JHXMLParser

@synthesize ident;

- (id)init {
    if ((self = [super init])) {
        ident = [[NSString alloc] init];
    }
    return self;
}

- (id)initWithKeyValuePair:(JHKeyValuePair *)kvPair {
    if ((self = [self init])) {
        _key = [kvPair key];
        _rawData = [kvPair value];
        _dataParser = [[NSXMLParser alloc] initWithData:_rawData];
        _dataParser.delegate = self;
    }
    return self;
}

- (id)initWithKey:(NSString *)key andData:(NSData *)data {
    if ((self = [self init])) {
        _key = key;
        _rawData = data;
        _dataParser = [[NSXMLParser alloc] initWithData:_rawData];
        _dataParser.delegate = self;
    }
    return self;
}

- (id <JHXMLParserDelegate>)delegate {
    id <JHXMLParserDelegate> d = nil;
    if (_delegate) {
        d = _delegate;
    }
    return d;
}
- (void)setDelegate:(id <JHXMLParserDelegate>)delegate {
    _delegate = delegate;
}

- (BOOL)start {
    return [_dataParser parse];
}

- (void)dealloc {
    [_parsedData release];
    [_rawData release];
    [super dealloc];
}

#pragma mark - NSXMLParser Delegate

- (void)parserDidStartDocument:(NSXMLParser *)parser {
    _parsedData = [[NSMutableArray alloc] init];
}

- (void)parser:(NSXMLParser *)parser didStartElement:(NSString *)elementName namespaceURI:(NSString *)namespaceURI qualifiedName:(NSString *)qualifiedName attributes:(NSDictionary *)attributeDict {
    _currentTag = elementName;
    if ([elementName isEqualToString:_key]) {
        NSMutableDictionary *tmpDict = [[NSMutableDictionary alloc] init];
        [_parsedData addObject:tmpDict];
        [tmpDict release];
    }
}

- (void)parser:(NSXMLParser *)parser foundCharacters:(NSString *)string {
    NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
    if (![_previousTag isEqualToString:_currentTag]) {
        [[_parsedData lastObject] setObject:[string stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceAndNewlineCharacterSet]]
                                     forKey:_currentTag];
    } else {
        [[_parsedData lastObject] setObject:[NSString stringWithFormat:@"%@%@",[[_parsedData lastObject] objectForKey:_currentTag], [string stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceAndNewlineCharacterSet]]] 
                                     forKey:_currentTag];
    }
    if (_previousTag) {
        [_previousTag release];
        _previousTag = nil;
    }
    _previousTag = [[NSString alloc] initWithFormat:@"%@", _currentTag];
    [pool drain];
}

- (void)parser:(NSXMLParser *)parser didEndElement:(NSString *)elementName namespaceURI:(NSString *)namespaceURI qualifiedName:(NSString *)qName {
    NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
    if (![_previousTag isEqualToString:elementName]) {
        [[_parsedData lastObject] setObject:@"" forKey:elementName];
    } else {
        if (_previousTag) {
            [_previousTag release];
            _previousTag = nil;
        }
        _previousTag = [[NSString alloc] initWithFormat:@""];
    }
    [pool drain];
}

- (void)parserDidEndDocument:(NSXMLParser *)parser {
    if ([_delegate respondsToSelector:@selector(acceptParsedData:withIdent:)]) {
        [_delegate acceptParsedData:_parsedData withIdent:ident];
    } else if ([_delegate respondsToSelector:@selector(acceptParsedDebugData:withIdent:)]) {
        [_delegate acceptParsedDebugData:_parsedData withIdent:ident];
    }
}

- (void)parser:(NSXMLParser *)parser parseErrorOccurred:(NSError *)parseError {
#ifdef DEBUG
    DEBUGLOG(@"Parser ERROR Occurred: %@", self.ident);
    DEBUGLOG(@"ERROR: %@", parseError);
#endif
    if ([_delegate respondsToSelector:@selector(acceptParsedData:withIdent:)]) {
        [_delegate acceptParsedData:_parsedData withIdent:ident];
    } else if ([_delegate respondsToSelector:@selector(acceptParsedDebugData:withIdent:)]) {
        [_delegate acceptParsedDebugData:_parsedData withIdent:ident];
    }
}

@end

Used like so:

parser = [[[JHXMLParser alloc] initWithKey:@"INFO" andData:connectData] autorelease];
parser.ident = @"INFO";
parser.delegate = self;
[parser start];

Then implement the delegate method:

- (void)acceptParsedData:(NSMutableArray *)parsedData withIdent:(NSString *)ident {
    // do stuff here with the parsed data
}