Objective-c NSMutableArray of Objects retain

Question

I just can't get it! I have custom class "Word" also I generate NSMutableArray of Word-class-objects in few steps:

words = [NSMutableArray array];
for i = 0 to 8
word = alloc+init;
[words addObject: word];
[word release];

Then I pass words instance to setter of another class:

someInstance.words = words;

Where words is nonatomic, retain property. I declare setWords method like this:

-(void)setWords:(NSMutableArray *)w {
    [w retain];
    [words release];
    words = w;
}

When words come to method as "w" variable it is an array of object but when I retain it and assign to my old value my words variable becomes an NSMUtableArray and it count is equal to w.count, but items of array 0x0. The "=" operator does not copy items of array, how can I fix it? Please help, I am a newbie in objective-c. I instanciate Word only with one method, shoud I implement parameterless init method?

-(id)initWithId:(int)Id Word:(NSString *)Word Card:(int)Card {
    self.id = Id;
    self.word = Word;
    self.card = Card;
    return self;
}

The cycle where I generate my NSMutableArray:

Card *card = [[Card alloc] initWithId:[s intForColumn:@"id"] Type:[s intForColumn:@"type"] Used:[s intForColumn:@"used"]];
s = [db executeQueryWithFormat:@"SELECT w.id as id, word, card FROM word as w INNER JOIN card as c ON w.card=c.id WHERE c.id=%i ORDER BY w.id, RANDOM()", card.id];
while ([s next]) {
    Word *word = [[Word alloc] initWithId:[s intForColumn:@"id"] Word:[s stringForColumn:@"word"] Card:[s intForColumn:@"card"]];
    [card.words addObject:word];
    [word release];
}

To understand you can look at screenshot I was not able to insert it in the post because of small reputation: i.sstatic.net/UheIk.png — Luft-on
– Luft-on, Commented Feb 8, 2012 at 21:26
Another idea is to use words = [w mutableCopy] in your setter method. — Rog
– Rog, Commented Feb 8, 2012 at 21:34
Can you please add the exact code you use to create this array before passing it to the setter? — jscs
– jscs, Commented Feb 8, 2012 at 21:35
@Rog: Not completely irrelevant; it still documents the behavior of the setter. — jscs
– jscs, Commented Feb 8, 2012 at 21:37

bbum · Accepted Answer · 2012-02-08 22:59:44Z

0

There are a number of problems w/your code.

you need to follow the standard initialization pattern of calling super's designated initializer and checking the return value.
That method should be named initWithId:word:card: (i.e. case is wrong, hence the goofy coloring on StackOverflow, even).
There is no need to implement a custom setter/getter if your setter/getter just follow the standard pattern. Use an @property and @synthesize.
(from your screenshot) you really don't want to be directly triggering UI updates from your setter. Generally, anyway. Generally, you want your view layer to trigger an update of your model through the control and, once the model is fully updated, then let the view layer know it should reload.
While you mention that you are instantiating an NSMutableArray instance, you don't show that in your code. Is card.words really set when you are adding Word instances?

Show the -initWithId:card:type:used: (note I corrected the case) method's implementation.

I.e. it better had have something like:

 words = [NSMutableArray new]; // Or, if ARC, [NSMutableArray array];

OK -- next...

put an assert(card.words); before your while() loop... that'll blow up if words isn't set.
make sure that the card is non-nil (no reason why it shouldn't but... when the obvious stuff looks right, you check the really obvious stuff next)

The comment about -reloadData is more that you would want to reloadData in whatever triggers the loading in the first place. Imagine a situation where you are loading several different kinds of data prior to updating the whole UI; maybe the table view has to be reloaded and some other stuff needs to be updated around it. By moving the reloadData out of the setter it (a) makes the setter simple and non-surprising while (b) makes it easier to refactor your UI layer such that multi-UI element updating can be done simultaneously.

(Also -- please don't take my comments about coding style harshly... not meant to be... there are some subtle, but universal patterns to Obj-C coding. If you learn them and use them, it'll make your life a lot easier. We were all new to Obj-C once. Just that some of us were new to it while others of your weren't even born yet. ;).

edited Feb 8, 2012 at 22:59

answered Feb 8, 2012 at 22:07

bbum

163k23 gold badges276 silver badges360 bronze badges

Sign up to request clarification or add additional context in comments.

3 Comments

Luft-on Over a year ago

-(id)initWithId:(int)i type:(int)t used:(int)u { self.id = i; self.type = t; self.used = u; self.words = [NSMutableArray array]; return self; }

Luft-on Over a year ago

1. I fixed it 2. Okay, my mistake, corrected 3. But I also want to execute [tableView reloadData] method 4. tableView is an UITableView, words is my data to fill table cells, isn't it nessesary to call reloadData when I update datasource? 5. Look prev comment

Luft-on Over a year ago

I make my assign working just removed @synthesize words statement and added NSMutableArray *words_, but now I can't make my tablwview updates with new datasource, even [tableView reloadData] not working =(

Collectives™ on Stack Overflow

Objective-c NSMutableArray of Objects retain

1 Answer 1

3 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

3 Comments

Your Answer

Sign up or log in

Post as a guest

Related