NSMutableArray Not Retaining Objects Outside Method [closed] - iphone

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Closed 9 years ago.
In my -viewDidLoad method, I initialize many NSMutableDictionaries, and add them to an initialized NSMutableArray declared via #property in the class header file. The relevant code is shown below. In short, I'm webscraping information from an HTML webpage.
NSMutableDictionary *dict = [[NSMutableDictionary alloc] init];
_regionalDicts = [[NSMutableArray alloc] init];
for (int i = 0; i < [strings count]; i++) {
NSString *str = [strings objectAtIndex:i];
//Property parser:
if ([str rangeOfString:#"<td>"].location != NSNotFound) {
NSString *parsedTD1 = [str stringByReplacingOccurrencesOfString:#"<td>" withString:#""];
NSString *parsedTD2 = [parsedTD1 stringByReplacingOccurrencesOfString:#"</td>" withString:#""];
NSString *parsedTD3 = [parsedTD2 stringByReplacingOccurrencesOfString:#" " withString:#"\n"];
NSString *final = [parsedTD3 stringByReplacingOccurrencesOfString:#"\t" withString:#""];
//NSLog(#"Final string: %#", final);
if ([final isEqualToString:#""]) {
continue;
}
if (gotEventType == NO) {
gotEventType = YES;
[dict setObject:final forKey:#"type"];
continue;
}
if (gotRegional == YES && gotLocation == NO) {
gotLocation = YES;
[dict setObject:final forKey:#"location"];
continue;
}
if (gotLocation == YES && gotCity == NO) {
gotCity = YES;
NSString *cityToReturn = [final stringByReplacingOccurrencesOfString:#"\n" withString:#""];
[dict setObject:cityToReturn forKey:#"city"];
continue;
}
if (gotRegional == YES && gotEventType == YES && gotCity == YES && gotLocation == YES && gotURL == YES) {
gotRegional = NO;
gotEventType = NO;
gotCity = NO;
gotLocation = NO;
gotURL = NO;
NSLog(#"Regional: %#", [dict objectForKey:#"regional"]);
NSLog(#"Type: %#", [dict objectForKey:#"type"]);
NSLog(#"City: %#", [dict objectForKey:#"city"]);
//Testing to see if anything is nil
NSLog(#"Location: %#\n", [dict objectForKey:#"location"]);
if (!_regionalDicts) {
NSLog(#"Dict is nil");
}
[_regionalDicts addObject:dict];
NSLog(#"Objects in array: %u", [_regionalDicts count]);
NSMutableDictionary *tempDict = [_regionalDicts objectAtIndex:[_regionalDicts count]-1];
NSLog(#"Regional in array: %#", [tempDict objectForKey:#"regional"]);
[dict removeAllObjects];
continue;
}
It's clear that the generated dictionaries are generated and retained within the _regionalDicts mutable array, which is declared in the header file like this:
#property (strong, nonatomic) IBOutlet NSMutableArray *regionalDicts;
However, when I attempt to pass in information to table view cells in in the same class, the dictionaries' contents are null. There are as many objects within the array as dictionaries I am expecting, but they do not contain any content.
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
static NSString *CellIdentifier = #"Cell";
UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier];
if (cell == nil) {
cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:CellIdentifier];
}
if (_regionalDicts) {
NSMutableDictionary *dict = [_regionalDicts objectAtIndex:0];
NSLog(#"Setting label %#", [dict objectForKey:#"city"]);
[cell.textLabel setText:[dict objectForKey:#"regional"]];
}
return cell;
}
Returns:
2013-04-01 19:58:50.250 MatchScrape[53570:207] Setting label (null)
I can only imagine that a memory management issue is to blame. Why would the contents of a class array be nullified when accessed outside the scope of the method they are added in, but allow the array to retain the same count?

Answer 1

You seem to believe that adding the dictionary to the array doesn't actually add the dictionary to the array, but instead adds a copy of the dictionary. You're probably thinking of how it might work in a language like C++ — but that isn't how it works here. Remember, Objective-C objects are always accessed by reference: you never directly store the object itself in a variable or array — you're just shuffling around a pointer to the actual object, which usually lives on the heap.
So when you add _dict to the array, the one in the array is the very same object referenced by _dict. Anything you do to that dictionary — no matter what reference you use — will be reflected everywhere else that dictionary is referenced, because it's the same dictionary. You haven't made a copy of it. Thus, when you do [_dict removeAllObjects], that removes all the objects from the dictionary and you end up with an array that contains the same empty dictionary a bunch of times.