Question

I have a NSMutableArray in my app which I initiate like this:

H-FILE

NSMutableArray *noteBookContent;
@property (nonatomic, retain) NSMutableArray *noteBookContent;

M-FILE

@synthesize noteBookContent;

I then have a method in which I open a txt file and read its contents into a temp NSString and slices this NSString into different bits which are then put into the NSMutableArray. Like so:

    NSString *tempTextOut = [NSString stringWithContentsOfFile:filePath
                                                          encoding:NSUTF8StringEncoding
                                                             error:&error];

self.noteBookContent = [[[tempTextOut componentsSeparatedByString: @"\n[DIVIDER]\n"] mutableCopy] autorelease];

My big question is what happens if I repeat the same process a couple of times. Is there a need to release the noteBookContent before I read new data into it? Is there a chance of data being messed up, e.g. if one noteBookContent has 10 items (all called FRUIT) and the next noteBookContent has 5 items (all called SALAD), may I end up with SALAD, SALAD, SALAD, SALAD, SALAD, FRUIT, FRUIT, FRUIT, FRUIT etc.?

Sorry if this is obvious, but I don’t really understand what happens in the moment that I read new data into an NSMutableArray which already contains old data.

Thanks for any explanations!

Answer 1

In this case you’re not actually changing the contents of the array—you’re replacing the object entirely. The old value of noteBookContent—the NSMutableArray instance—gets released by the property assignment (the .noteBookContent = ...), and replaced with a new, separate NSMutableArray that’s created by the -mutableCopy call. A more efficient way to do it would be this:

[self.noteBookContent removeAllObjects];
[self.noteBookContent addObjectsFromArray:[tempTextOut componentsSeparatedByString: @"\n[DIVIDER]\n"]];