Checking if an array contains a certain object (iOS)

Question

I need to check if a certain array contains a certain object, and if it does, delete that object. If it hasn't got that object, the funciton is suposed to add it into the array. The problem is that the object is always added because the checking statement always return false.

Here's my current function:

- (void) myFunction:(NSString *)parameter {

    if (![myMutableArray containsObject:parameter]) {

        [myMutableArray addObject:parameter];
        NSLog(@"%@ added", parameter);

    } else {

        [myMutableArray removeObject:parameter];
        NSLog(@"%@ deleted", parameter);

    }
}

I suspect you are having the same issue as was solved in this question: http://stackoverflow.com/questions/2941596/nsarray-containobjects-method — Paul O., Jan 16 '13 at 19:18
What happens if you call your method twice with the same parameter? — Hot Licks, Jan 16 '13 at 19:21
Do you want to check if you have the same object (meaning same memory address, etc) or just an equal string (like @"a" 'is equal to' @"a")? — Alex, Jan 16 '13 at 19:25
Yes, all objects are strings and when I try to call the method twice with the same parameter, I just return `deleted` in my console — iosdevrocks, Jan 16 '13 at 19:25
That would suggest that your original string and the new one are different somehow -- case, whitespace, etc. — Hot Licks, Jan 16 '13 at 19:28
Your code works with 2 different arrays: `myMutableArray` and `myMutbaleArray`. That would explain the problem if it is your actual code. — Martin R, Jan 16 '13 at 19:29
@iosdevrocks: It is always better to copy/paste the actual code into the question, instead of re-typing it. — Martin R, Jan 16 '13 at 19:40
I've checked again the code and I've realized that the problem is that any object is added. Maybe the problem is in the `addObject` function. Is it possible? — iosdevrocks, Jan 16 '13 at 19:40
Have you verified that myMutableArray is *allocated+initialized*? (See mprivat's answer.) — Martin R, Jan 16 '13 at 19:41
Yes it was instantiated but the function wasn't called due to another issue that I've just fixed. Thanks! Problem solved — iosdevrocks, Jan 16 '13 at 19:47
For future folks that may encounter similar symptoms, what "issue" did you find? — Hot Licks, Jan 16 '13 at 20:21

score 33 · Accepted Answer · answered Jan 16 '13 at 19:23

containsObject is calling isEqual on each of the object in the arrays. What type of object are you checking for? If it's a custom object, override and implement the method isEqual.

I'm guessing you're trying to check the value of the object, but containsObject is actually calling isEqual which is comparing the reference to the object, and not its actual value.

score 20 · Answer 2 · answered Mar 04 '14 at 05:45

20

if (![arrList containsObject:arrObj]) {
    // do something
}

containsObject:

answered Mar 04 '14 at 05:45

Darshit Shah

2,366
26
33

score 7 · Answer 3 · answered Jan 16 '13 at 19:58

First you need to check which type data or object you are adding in this myMutableArray. According to your method you are checking in mutable array for string type that you have passed argument parameter. It may be possible that you are containing int or float array.

There may be issue of type casting in your array.If your is STRING type of data then you can use another method like this.

- (void) myFunction:(NSString *)parameter {

for (int i = 0 ; i < [myMutableArray count ] ; i++) {


    if (![[myMutableArray objectAtIndex:i] isEqualToString:parameter]) {
        [myMutableArray addObject:parameter];
        NSLog(@"%@ added", parameter);
    }
    else{
        [myMutableArray removeObject:parameter];
        NSLog(@"%@ deleted", parameter);
    }
}

}

Hope this will help you. If your object is not type of NSString then you need to convert.

Attila H · Answer 4 · 2013-01-16T19:34:10.710

2

You should implement isEqual: in your custom class. By default two objects are only identical if they share the same reference.

Also make sure to initialize your mutable array before using it.

EDIT:

It seems that your array's variable name are most probably mistyped.

myMutableArray
myMutbaleArray

edited Jan 16 '13 at 19:34

answered Jan 16 '13 at 19:21

Attila H

3,616
2
24
37

It's not a custom class, it's a NSString – mprivat Jan 16 '13 at 19:21

mprivat · Answer 5 · 2013-01-16T19:29:41.167

You probably forgot to initialize your NSMutableArray. If not initialized, you are sending addObject messages to a nil object, which has no effect, and the array never contains what you previously added...

Of course, if the array is nil, then the contains check will always return false. According to the Objective-C docs:

If the method returns an object, any pointer type, any integer scalar of size less than or equal to sizeof(void*), a float, a double, a long double, or a long long, then a message sent to nil returns 0.

And 0 is false

Checking if an array contains a certain object (iOS)

5 Answers5