I have a custom object called Person
that among other things contains an NSString
field called descriptor
, which stores what sort of person that Person
object is (angry, sad, wild, happy, morose, etc). All of my Person objects are in an NSMutableArray
, but I would like to store them in an NSMutableDictionary
in such a manner:
Key: A, Object: An NSMutableArray
where all Person
objects have descriptor
starting with 'A'
Key: B, Object: An NSMutableArray
where all Person
objects have descriptor
starting with 'B'
Key: C, Object: An NSMutableArray
where all Person
objects have descriptor
starting with 'C'
etc...
I've tried to do this in my code below, and at the comment //POINT 1, the keys and arrays seem to match up, but at //POINT 2, when I print out the complete dictionary, all the keys come up with the same values!
So I wanted to know why the NSMutableArray
I seem to have is not being stored as I want it in the NSMutableDictionary
?
- (void)buildDictionaryForIndexList {NSMutableDictionary *tempDict = [[[NSMutableDictionary alloc] init] autorelease];
NSMutableArray *personsStartingWithLetter = [[NSMutableArray alloc] init];
NSMutableArray *indexList = [[[NSMutableArray alloc] init] autorelease];
NSInteger loopCounter = 1;
NSString *firstLetter = [[[NSString alloc] init] autorelease];
for (Person *v in persons) {
firstLetter = [[v descriptor] substringWithRange:NSMakeRange(0, 1)];
if ([indexList containsObject:firstLetter]) {
[personsStartingWithLetter addObject:v];
if (loopCounter == [persons count]) {
[tempDict setObject:personsStartingWithLetter forKey:firstLetter];
}
} else {
if (loopCounter > 1) {
//POINT 1
NSLog(@"%@",[indexList objectAtIndex:[indexList count]-1]);
for (Person *q in personsStartingWithLetter) {
NSLog(@"%@",[q descriptor]);
}
[tempDict setObject:personsStartingWithLetter forKey:[indexList objectAtIndex:([indexList count] - 1)]];
[personsStartingWithLetter removeAllObjects];
}
[indexList addObject:firstLetter];
[personsStartingWithLetter addObject:v];
} // else
loopCounter++;
} // for
//POINT 2
NSEnumerator *enumerator = [tempDict keyEnumerator];
for (NSString *str in enumerator) {
NSLog(@"%@",str);
for (Person *c in [tempDict objectForKey:str]) {
NSLog(@"%@",[c descriptor]);
}
}
self.dictionary = tempDict;
} // buildDictionaryForIndexList
So, for example, at POINT 1 my output is:
A
Angry
Amiable
B
Belligerent
C
Cool
...
W
Wild
but at POINT 2 my output is
T
Wild
J
Wild
A
Wild
...
W
Wild
Change [tempDict setObject:personsStartingWithLetter forKey:[indexList objectAtIndex:([indexList count] - 1)]];
(just after point 1) to [tempDict setObject:[[personsStartingWithLetter copy] autorelease] forKey:[indexList objectAtIndex:([indexList count] - 1)]];
. The problem is that NSDictionary copies the key, but retains the value. Therefore, if you add a mutable array to the dictionary and then change it, the array in the dictionary also changes. You need to create a non-mutable copy of the array to put in the dictionary.
The whole method is a bit overcomplicated.
- (void)buildDictionaryForIndexList
{
NSMutableDictionary *tempDict = [[[NSMutableDictionary alloc] init] autorelease];
for (Person *v in persons)
{
NSString* firstLetter = [[v descriptor] substringWithRange:NSMakeRange(0, 1)];
NSMutableArray* personsStartingWithLetter = tempDict [firstLetter];
if (personsStartingWithLetter == nil)
{
personsStartingWithLetter = [NSMutableArray array];
tempDict [firstLetter] = personsStartingWithLetter;
}
[personsStartingWithLetter addObject:v];
} // for
self.dictionary = tempDict;
}
You start with an empty dictionary that will contain arrays. For every person, you check whether there is a suitable array or not, and if there isn't one, you create it. So now there is an array for the person, so you add it to the array. That's all.