Objective-C :: using a method to change an object

Question

I have a class called "CardSet", containing an NSMutableArray* cardSet to hold "cards", which I extend to make "DeckCards". I'd like "CardSet" to have a method called "(void)addCard:(Card*)" (and similarly a method "removeCard"). I'd like "addCard" to some how have access to and set cardSet. Even better I'd like to use the "addCard" method to initialise cardSet. The class file "CardSet.h" reads:

 #import < Cocoa/Cocoa.h >

 #import < Card.h >

@interface CardSet : NSObject {

    NSMutableArray* cardSet;

}

-(id)init;

-(NSMutableArray*)getCardSet;

-(void)setCardSet:(NSMutableArray *)new_cardset;

-(Card*)getCard:(NSInteger) index;

**-(void)addCard:(Card*) new_card;**

-(void)removeCard:(Card*) old_card;

-(void)dealloc;

@property (readwrite, retain, getter=getCardSet, setter=setCardSet) NSMutableArray* cardSet;

@end

and the method file reads:

 #import "CardSet.h"

@implementation CardSet

-(id)init{
    if( self = [super init] ){}   //will add initialisations here later
    return self;
}

-(NSMutableArray*)getCardSet{
    return cardSet;
}

-(void)setCardSet:(NSMutableArray *)new_cardSet{
    cardSet = new_cardSet;
}

-(Card*)getCard:(NSInteger)index{
    return [cardSet objectAtIndex:index];
}

**-(void)addCard:(Card *)new_card{
    [cardSet addObject:new_card];
}**

-(void)removeCard:(Card *)old_card{
    [cardSet removeObject:old_card];
}

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

@synthesize cardSet;

@end

This compiles just fine. I'd like to initialise a "DeckCards" instance using its "addCard" method 52 times. When I call addCard 52 times in a DeckCards setter method, and ask for the size of its "cardSet", I'm returned 0.

This appears to be a scope or privileges problem? Can the "addCard" method have any setter privileges? Must a setter argument be the same as the return and respective member type?

[I can work around the above by creating an NSMutableArray object "deck_cards_temp" outside of "DeckCard", add 52 cards to this, and pass it to set the member of my "DeckCards" instance via the setter inherited from "CardSet". This is not very satisfactory!]

What do you advise? Many thanks in advance for your help and patience.

Answer 1

You are never actually creating the cardSet object. You should be creating it in your -init method:

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

Because you never actually create the array, all the calls to -addCard: are being sent to a nil object.

When you pass in an array to -setCardSet:, you are passing in an initialized array so the array is no longer nil and the -addCard: calls work fine.

Answer 2

CardSet.h

#import <Cocoa/Cocoa.h>

// For know we just need to know there is a class named "Card" being used but implemented later
@class Card;

@interface CardSet : NSObject {
    NSMutableArray *cardSet;
}

// Here are the methods according to "correct" naming conventions
- (Card *)cardAtIndex:(NSInteger)index;
- (void)addCard:(Card *)card;
- (void)removeCard:(Card *)card;

// This will help us and forget about writing the setter/getter
@property (nonatomic, retain) NSMutableArray *cardSet;

@end

CardSet.m

#import "CardSet.h"
// Now we tell the compiler what "Card" is and what methods etc. it has
#import "Card.h"

@implementation CardSet

@synthesize cardSet;

- (id)init {
    if (self = [super init]) {
        // If we don't create the cardSet, how are we able to work with it!?
        NSMutableArray *anArray = [[NSMutableArray alloc] init];
        self.cardSet = anArray;
        [anArray release];
    }
    return self;
}

- (Card *)cardAtIndex:(NSInteger)index {
    return [cardSet objectAtIndex:index];
}

- (void)addCard:(Card *)card {
    [cardSet addObject:card];
}

- (void)removeCard:(Card *)card {
    [cardSet removeObject:card];
}

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

@end

As Abizern already noted: Naming the array the same as your class is a bad thing.

Answer 3

I would shorten that init method:

- (id)init {
    if (self = [super init]) {
        // If we don't create the cardSet, how are we able to work with it!?
        self.cardSet = [NSMutableArray array];
    }
    return self;
}