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POIOS 5: How to return YES on contains: with 2 'identical' objects, but with different pointers
 

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  1. POIOS 5: How to return YES on contains: with 2 'identical' objects, but with different pointers
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    <p>I'm quite new to StackOverflow, so apologies in advance if I forgot some critical element in my question. It's a long one, so bear with me!</p> <p><strong>Iterating over JSON-webservice result:</strong></p> <p>For an IOS5 iPad app, I collect JSON information from a webservice and via: </p> <pre><code>NSData *data = [NSData dataWithContentsOfURL:url]; NSDictionary *json = [NSJSONSerialization JSONObjectWithData:data options:kNilOptions error:&amp;error]; </code></pre> <p>I'll iterate over the returned <code>NSDictionary</code> and store the returned objects and their properties as a custom class.</p> <p>The custom class contains several properties, including an <code>AmountInShoppingCart</code>-value.</p> <p>I use this custom class to represent items that we sell in our store, so an <code>NSMutableArray</code> is made of all the returned objects and shown to the user. If the <code>AmountInShoppingCart value &gt; 0</code>, then the object will be put in the <code>ShoppingCart</code> <code>NSMutableArray</code> (which is a singleton).</p> <p><strong>Checking for duplicates in ShoppingCart:</strong></p> <p>To make sure the <code>ShoppingCart</code> doesn't contain any duplicate entries, I've got a function like this in the <code>ShoppingCartController</code> (also borrowed from SO):</p> <pre><code>- (void)checkForDuplicates { NSMutableSet *seen = [NSMutableSet set]; NSUInteger i = 0; NSLog(@"ShoppingCartArray count: %u",[ShoppingCartArray count]); //Iterate over the Array to check for duplicates, and to sync the list with the cart. while (i &lt; [ShoppingCartArray count]) { id obj = [ShoppingCartArray objectAtIndex:i]; if ([seen containsObject:obj]) { if ([obj isKindOfClass:[MyCust class]]){ MyCust *cust = [ShoppingCartArray objectAtIndex:i]; MyCust *seenCust = [seen member:obj]; seenCust.AmountInShoppingCart = cust.AmountInShoppingCart; [ShoppingCartArray removeObjectAtIndex:i]; }} else {seen addObject:obj]; i++;}}} </code></pre> <p><strong>Equality &amp; Hashing</strong></p> <p>To accomplish this, I've overridden the <code>isEqual:</code>-function of the <code>MyCust</code>-class so that it'll look at the <code>externalItemID</code>-property, which is the only property that is definitely unique for each class object. </p> <p>I picked this function up from StackOverflow:</p> <pre><code>- (BOOL)isEqual:(id)otherObject; { if ([otherObject isKindOfClass:[MyCust class]]) { MyCust *otherCust= (MyCust *)otherObject; if (externalItemId != [otherCust externalItemId]) return NO; return YES; } return NO; } - (NSUInteger) hash; { return [[self externalItemId] hash]; } </code></pre> <p><strong>Sync the two arrays:</strong></p> <p>It can happen that people request the same result from the JSON-webservice, since it uses the MyCust's size, height and diameter to return a set of objects that adhere to those sizes.</p> <p>So I use the following function to check and 'sync' the two NSMutableArrays with the new results:</p> <pre><code>In: RESULTLISTCONTROLLER.M - (void) syncWithCart { ShoppingCart *sc = [ShoppingCart sharedCart]; [sc checkForDuplicates]; NSMutableSet *listSet = [NSMutableSet setWithArray:resultList]; NSUInteger i = 0; while (i &lt; [sc.ShoppingCartArray count]) { id ShopObject = [sc.ShoppingCartArray objectAtIndex:i]; if ([listSet containsObject:ShopObject]) { MyCust *listCust = [listSet member:ShopObject]; MyCust *shopCust = ShopObject; listCust.AmountInShoppingCart = shopCust.AmountInShoppingCart; [listSet removeObject:ShopObject]; } else {i++;}}} </code></pre> <p>This all works pretty well until...</p> <p><strong>The 2nd webservice!</strong></p> <p>Now here comes the good part: There's a 2nd JSON-WebService the app uses to retrieve external supplier stock. It sometimes contains the same <code>MyCust</code> objects, but contains extra information that has to be parsed into the existing objects.</p> <p>I basically get the first WebService's result into the <code>getMyCustArray</code> and the other in the <code>getExternalCustArray</code>. I then check if <code>getMyCustArray</code> contains an object in the <code>getExternalCustArray</code> and update the additional information on the objects and delete the similar object in <code>getExternalCustArray</code>. Any leftover objects only available from the supplier will be added using:</p> <pre><code>mergedCustArray = [NSMutableArray arrayWithArray:[getMyCustArray arrayByAddingObjectsFromArray:getExternalCustArray]]; </code></pre> <p>Now the problem is, that when the user checks the same sizes twice, the App doesn't seem to consider the new results as the same.</p> <p>When I do an NSLog of the ShoppingCartArray, the following shows: (original item names obfuscated)</p> <p><strong>First Search:</strong></p> <pre><code>MyCust: SideShowBobsEarWarmers Hash: **2082010619** AmountInShoppingCart: 4 **&lt;MyCust: 0x81cee50&gt;**", " MyCust: SolidSnakesCardBoardBox Hash: **4174540990** AmountInShoppingCart: 4 **&lt;MyCust: 0x8190d10&gt;**" </code></pre> <p><strong>Second Search:</strong> the ResultList doesn't retain the MyCust's AmountInShoppingCart values, so I add them to the ShoppingCart again from the ResultList.</p> <pre><code> MyCust: SideShowBobsEarWarmers Hash: **2082010619** AmountInShoppingCart: 4 **&lt;MyCust: 0x81cee50&gt;**", MyCust: SolidSnakesCardBoardBox Hash: **4174540990** AmountInShoppingCart: 4 **&lt;MyCust: 0x8190d10&gt;**" " // Different Pointers, although they should be considered Equal. MyCust: SideShowBobsEarWarmers Hash: **2082010619** AantalInWinkelWagen: 3 **&lt;MyCust: 0x74bc570&gt;**", " MyCust: SolidSnakesCardBoardBox Hash: **4174540990** AantalInWinkelWagen: 2 **&lt;MyCust: 0x74bc7b0&gt;**" </code></pre> <p>So somehow the compiler allocates those objects in a different memory address/pointer, and then breaks the <code>isEqual:</code> function, as far as I can tell.</p> <p>My guts tell me there's something to do with <code>NSCopy(able)</code>, but I'm not quite sure how I'd implement that. If anyone got some good tips for a Shopping Cart system, that's always welcome too. I've got half a mind converting all this to Core Data but would like to have the core functionality in place before doing that.</p>
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    1. COI changed the `isEqual` method to: `-(BOOL) isEqual: (id) rhs { //Overriding isEqual to make sure MyCust returned from the webservice are equal to the ones already in the shoppingcart or list BOOL ret = NO; if ([rhs isKindOfClass: [MyCust class]]) // do not use [self class] { ret = [self externalItemId] == [rhs externalItemId]; } return ret; } -(NSUInteger) hash { return [[self externalItemId] hash]; }`
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    2. CODidn't work either.
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