Objective C: Passing NSDictionary from One Class to Another - iphone

Question

All,
Disclaimer: I'm aware that there are other questions that ask similar questions, but none provide an answer that I understand or an answer that applies to my situation.
I have two classes, classA and classB. In classA there is a void instance method that creates a NSMutableDictionary (if you want specifics, it's a XMLparser). After classA's XMLParser is run and the NSMutableDictionary has been created and filled, classB is called which needs to do some other things with that dictionary. For some reason, classB cannot access the NSMutableDictionary in classA (actually, it can access it, but for some reason it shows up as "NULL"). What should I do?
Thanks in advance.
EDIT: You asked for the source code, you got it. ClassA below, dictionary in question is called "response."
#import "XMLParser.h"
#import "CardSetupViewController.h"
#implementation XMLParser
#synthesize response;
- (XMLParser *) initXMLParser
{
self = [super init];
// init dictionary of response data
response = [[NSMutableDictionary alloc] init];
return self;
}
//Gets Start Element of SessionData
- (void)parser:(NSXMLParser *)parser
didStartElement:(NSString *)elementName
namespaceURI:(NSString *)namespaceURI
qualifiedName:(NSString *)qualifiedName
attributes:(NSDictionary *)attributeDict
{
if ([elementName isEqualToString:#"SessionData"])
{
NSLog(#"Found SessionData in the return XML! Continuing...");
//response is a NSMutableArray instance variable
//THIS SHOULD NEVER NEED TO BE USED
if (!response)//if array is empty, it makes it!
{
NSLog(#"Dictionary is empty for some reason, creating...");
response = [[NSMutableDictionary alloc] init];
}
//END: THIS SHOULD NEVER BE USED
return;
}
else
{
currentElementName = elementName;
NSLog(#"Current Element Name = %#", currentElementName);
return;
}
}
- (void)parser:(NSXMLParser *)parser foundCharacters:(NSString *)string
{
if (!currentElementValue) {
// init the ad hoc string with the value
currentElementValue = [[NSMutableString alloc] initWithString:string];
} else {
[currentElementValue setString:string];
NSLog(#"Processing value for : %#", string);
}
}
//Gets End Element of SessionData
- (void)parser:(NSXMLParser *)parser
didEndElement:(NSString *)elementName
namespaceURI:(NSString *)namespaceURI
qualifiedName:(NSString *)qName {
if ([elementName isEqualToString:#"SessionData"])
{
// We reached the end of the XML document
// dumps dictionary into log
NSLog(#"Dump:%#", [response description]);
return;
}
else
{
//Adds key and object to dictionary
[response setObject:currentElementValue forKey:currentElementName];
NSLog(#"Set values, going around again... brb.");
}
currentElementValue = nil;
currentElementName = nil;
}
#end

Answer 1

You probably want to look into using singletons.
http://www.galloway.me.uk/tutorials/singleton-classes/
http://pixeleap.com/?p=19
http://www.iphonedevsdk.com/forum/iphone-sdk-development/5302-how-make-global-variables-objectivec.html
Those should get you started, if you need clarification just ask.

Answer 2

Are currentElementName and currentElementValue ivars ? If so, every time you catch either an element or a value, you must then release your ivar and retain the new value you catch.
Also, as the comments are saying you didn't follow any rules about writing a correct initializer.
What about classB ? Isn't there some logic that makes your dictionary be released ?
Try managing a bit more the memory.

Answer 3

you have several options... so many options actually
Option A:(set)
#interface ClassB{
NSDictionary * someDict;
}
-(void)setSomeDict:(NSDictionary *)aDict;
#end
#implementation ClassB
-(void)setSomeDict:(NSDictionary *)aDict
{
someDict = [aDict retain];//or copy depending on your needs;
}
#end
somewhere in ClassA...
ClassB * b = [ClassB new];
[b setSomeDict: someOtherDict];
Option B:(push)
#interface ClassB{
NSDictionary * someDict;
}
-(void)doSomethingWithDict:(NSDictionary *)aDict;
#end
#implementation ClassB
-(void)doSomethingWithDict:(NSDictionary *)aDict
{
NSLog(#"did something with aDict: %#",aDict);
}
#end
somewhere in ClassA...
ClassB * b = [ClassB new];
[b doSomethingWithDict: someOtherDict];
Option c:(init)
#interface ClassB{
NSDictionary * someDict;
}
-(id)initWithDict:(NSDictionary *)aDict;
#end
#implementation ClassB
-(id)initWithDict:(NSDictionary *)aDict
{
self = [super init];
if(self)
{
someDict = [someDict retain]; //or copy depending on your needs
}
NSLog(#"did something with aDict: %#",aDict);
}
#end
somewhere in ClassA...
ClassB * b = [[ClassB alloc] initWithDict:someOtherDict];
[b doSomethingelse];
you can also use properties etc... there are many many options, but you should understand object ownership as well so you don't end up leaking the dictionary.
-(void)dealloc
{
[someDict release];
}
should be added to the classB.

Answer 4

First of all check if u get the response in this delegate method of NSXMLParser
- (void)parserDidEndDocument:(NSXMLParser *)parser;
and send the response via a delegate (which u should implement in this class) and the delegate method is to implemented in the other class ...Simple !!!