Add an argument to a protocol (delegate)

Question

I want to add an argument to a delegate methode (From NSXMLParserDelegate)

this is the method so far :

- (void)parser:(NSXMLParser *)parser foundCharacters:(NSString *)string{
    // save the characters for the current item...
    if ([string   isEqual: @"off"]) {
         myObject.isON = NO; //doesn't know what is myObject
    }

What I want :

- (void)parser:(NSXMLParser *)parser foundCharacters:(NSString *)string:(MyObject*)anObject{
    // save the characters for the current item...
    if ([string   isEqual: @"off"]) {
         anObject.isON = NO;
    }

Thank you

can you elaborate the exact requirement of having the object passed as an argument — Ratikanta Patra, Feb 27 '14 at 12:10
There can be some other ways of achieving this. It all depends on your requirement — Ratikanta Patra, Feb 27 '14 at 12:14
I can't change the XMLParser delegate method , If i do that it will not be called — The Fonz, Feb 27 '14 at 12:16
why not make "anObject" a instance variable using @property, so it is accessible all over the current class and in your method use it as `self.anObject.isON = NO;` — Sathya, Feb 27 '14 at 12:17
because I called the xmlparser delegates methods from an asynchronous request . It should know what object should be used or not — The Fonz, Feb 27 '14 at 12:19
i would recommend restructuring your code but if you want to go with your current code you can try the 'objc_setAssociatedObject' using this you can add your 'anObject' to the 'parser' and access it later. see http://oleb.net/blog/2011/05/faking-ivars-in-objc-categories-with-associative-references/ — Sathya, Feb 27 '14 at 12:26

score 1 · Accepted Answer · answered Feb 27 '14 at 12:23

First you need to subclass your NSXMLParser, add new delegate property call it subclassDelegate or something similar, so you can differentiate between the super class's delegate. In init be the delegate of your superclass self.delegate = self;

respond to the delegate methods and forward the methods that you don't want to override to the self.subclassDelegate respond to the method that you want to override and override it in your subclass protocol.

Here is the example:

    @protocol  MyXMLParserDelegate;
@interface MyXMLParser : NSXMLParser<NSXMLParserDelegate>
@property (weak) id<MyXMLParserDelegate> subclassDelegate;
@end

@protocol  MyXMLParserDelegate <NSObject>
- (void)parserDidStartDocument:(NSXMLParser *)parser;
// this is the method that you override
- (void)parser:(NSXMLParser *)parser foundCharacters:(NSString *)string withObject:(id)object;
@end

Then in .m

@implementation MyXMLParser

- (id)init
{
    self = [super init];
    if(self) {
        self.delegate = self;
    }
    return self;
}


#pragma mark - repspond to NSXMLParser delegate

- (void)parser:(NSXMLParser *)parser foundCharacters:(NSString *)string
{
    [self.subclassDelegate parser:parser foundCharacters:string withObject:yourObject];
}

@Max Puis, do you like this solution ? have you tried it out ? — Basheer_CAD, Feb 27 '14 at 12:56
Yes I tried but it doesn't works . I can't set my delegate here : MyXMLParser *parser = [[MyXMLParser alloc] initWithData:data]; [parser setDelegate:self]; — The Fonz, Feb 27 '14 at 13:13
you create your myNSXMLParser and then, instead of [parser setDelegate:self]; you do parser.subclassDelegate = self; — Basheer_CAD, Feb 27 '14 at 13:19
Thank you, but when I call [parser parse]; should I do [parser parse:myObject]; ? — The Fonz, Feb 27 '14 at 13:31

Add an argument to a protocol (delegate)

1 Answers1