NSDictionary functionality question

Question

Hello All,

So I am trying to save arrays into an NSDictionary on the fly. Let me show you the code and explain what is going on.

for (int x= 0; x <[appDelegate.people count]; x++) {
    Person *aPerson = [[Person alloc] init];
    aPerson = [appDelegate.people objectAtIndex:x];
    if ([appDelegate.groupedBusiness objectForKey:aPerson.business_name] == nil) {
        NSMutableArray *newBusiness = [[NSMutableArray alloc] init];
        //if the business does not exist in the dict, add the person to the business and add it to dict.

                    [newBusiness addObject:aPerson];

        [appDelegate.groupedBusiness setObject:newBusiness forKey:aPerson.business_name];

        [newBusiness release];
        newBusiness = nil;
        //NSLog(@"%@", appDelegate.groupedBusiness);
    } else {
        NSMutableArray *existingBusiness= [appDelegate.groupedBusiness objectForKey:aPerson.business_name];
        [existingBusiness addObject:aPerson];
                  //THIS IS THE LINE I AM NOT SURE ABOUT!!!
        [appDelegate.groupedBusiness setObject:existingBusiness forKey:aPerson.business_name];

        [existingBusiness release];
        existingBusiness = nil;
        //NSLog(@"%@", appDelegate.groupedBusiness);
    }

}

Alright, so the appDelegate has an array of "People" that has a whole bunch of attributes about a person. I am trying to set up a dictionary to sort them by their business names. I am doing this by creating an array and saving it in the dictionary with the business_name as the key. Each iteration of the loop I check to see if the key exists, if it does, pull out the existing array, add the person you are checking, and resave it to the dictionary. However, this does not appear to be happening. Is there some exotic behavior in the NSDictionary class that would prevent that? I have poured over the class web page and can't find anything. Sorry if this is a noobie question, I am still trying to understand the objective-c classes. Thanks!

Answer 1

Why do you release existingBusiness? You are not creating an object, just taking the pointer from an array. When you invoke release, retainCount became 0 and object deallocs.

Just remove the following two lines:

[existingBusiness release];
existingBusiness = nil;

and everything should work fine.

Answer 2

    [appDelegate.groupedBusiness setObject:existingBusiness forKey:aPerson.business_name];

    [existingBusiness release];
    existingBusiness = nil;

This should all be removed. existingBusiness is already in the dict, and it's a mutable object - when you're adding a person to it, this will be reflected in the dictionary as well as it's the same object you're dealing with. Apart from that you have a couple of memory leaks as Daniel points out.

Answer 3

You're way overcomplicating this, not to mention leaking a couple things.

for (Person *aPerson in appDelegate.people) {
    NSMutableArray *business = [appDelegate.groupedBusiness objectForKey:aPerson.business_name];
    if (!business) {
        business = [NSMutableArray array];
        [appDelegate.groupedBusiness setObject:business forKey:aPerson.business_name];
    }

    [business addObject:aPerson];
}

Answer 4

Not an answer, but some coding style issues.

Use fast iteration if you don't need the index:

for (Person *aPerson in appDelegate.people) {

Use convenience constructors; it makes your code more readable (remember to remove the "release" at the end):

NSMutableArray *newBusiness = [NSMutableArray arrayWithObject:aPerson];

Avoid duplicate logic where possible:

NSMutableArray * business = [appDelegate.groupedBusiness objectForKey:aPerson.business_name;
if (!business) {
  business = [NSMutableArray array];
}
[business addObject:aPerson];
[appDelegate.groupedBusiness setObject:business forKey:aPerson.business_name];

The "setObject:existingBusiness" call does changes nothing apart from wasting CPU cycles, but in the case above, it makes the code somewhat more readable.