Q:

Create an NSMutableArray that contains several NSMutableDictionary objects

I've looked around and seen several postings concerning sorting NSMutableArray's that contain NSDictionaries, but haven't been able to find some concrete examples of how to actually make an NSMutableArray composed of NSDictionaries. 
I am using NSUserDefaults to keep track of a user's preferences for several different items. The NSMutableArray will be used to keep track of the total items, and the NSDictionaries are for the individual preferences concerning each item.
I've written these methods to keep track of items in my preferences class, but I'm not too sure how to initialize the NMutableArray to contain NSDictionaries.
-(NSMutableArray *)deviceListArray
{
    return [[NSUserDefaults standardUserDefaults] mutableArrayValueForKey:@"device_list_array"];
}

-(void) setDeviceListArray:(NSMutableArray *)deviceListArray
{
    [[NSUserDefaults standardUserDefaults] setObject:deviceListArray forKey:@"device_list_array"];
}

If anyone could point me in the right direction, I would really appreciate it. Thank you very much! Or if someone has a better strategy for keeping track of items, each with different preferences, then that would be awesome too!
Thanks!!

A:

Once you hand an object of to userDefaults, it owns that object - so you cannot go changing properties of dictionaries inside it.
What you can do is a two pass copy, where you have a local mutable array with mutable dictionaries in it. You would create a new mutable array of the same size, then for each mutable dictionary, call [NSDictionary dictionaryWithDictionary:], adding the new non-mutable dictionary to the new array.
If you have mutable objects buried in the dictionaries, well, you need to do the same for that.
All that said, if you have such a huge amount of stuff I suspect you have no properly thought of how to use the defaults system. I almost always just save strings, numbers, colors etc.
EDIT: code
NSMutableArray *array = [NSMutableArray arrayWithCapacity:10];

for(int i=0; i<10; ++i) {
  NSMutableDictionary *dict = [NSMutableDictionary dictionaryWithCapacity:10];
  // add stuff to the dictionary
  [array addObject:dict];
}

// later on want to change second dictionary:
NSMutableDictionary *dict = [array objectAtIndex:1];
// fool around with dict
// no need to re-save it in array, since its mutable

