Question

In the following code I want to traverse an NSMutableArray (self.codes) which contains NSMutableDictionary objects. If the value for the “selected” key is equal to “1” then I want to copy the NSMutableDictionary “code” object and add it to the selectedCodes array.

1  -(NSMutableArray *)getSelecedCodes{
2  
3  NSMutableArray *selectedCodes=[[NSMutableArray alloc]init];
4  
5  for (NSMutableDictionary *code in self.codes) {
6    if([code valueForKey:@"selected"]==@"1"){
7      [selectedCodes addObject:[code copy]];
8    }
9  }
10
11 return selectedCodes;
12
13 }

When I analyze the code in XCode I get a warning of the potential memory leaks. Any thoughts on what I am doing wrong?

Answer 1

-[NSMutableArray addObject:] retains its argument. copy returns a retained value as well. So you’re retaining the copied dictionary twice.

You probably want to do this:

[selectedCodes addObject:[[code copy] autorelease]];

However, depending on your specific needs, there are a couple caveats:

1. Are you sure you want to copy the dictionary? You can just add it to the array:

   [selectedCodes addObject:code];

   Note that both selectedCodes and self.codes will contain pointers to the same dictionary, so changes in one copy will be reflected in the other as well.

2. You might want to create a mutable copy of the dictionary. copy returns an immutable object:

   [selectedCodes addObject:[[code mutableCopy] autorelease]];