Got exception when i try to replace a Mutable Array item

Question

i got this exception:

[__NSArrayI replaceObjectAtIndex:withObject:]: unrecognized selector sent to instance

when i try to replace a specific element by another:

EDIT: this is my whole code:

//declaring an AppDelegate instance
    AppDelegate *myAppDelegate=(AppDelegate *)[[UIApplication sharedApplication]delegate];

    //get the array in which we have stored all the choosed themes
    NSMutableArray *aMutableArray=myAppDelegate.themesChoosed;


    for (int i=0; i<[aMutableArray count]; i++) {
            NSString *str=[NSString stringWithString:[aMutableArray objectAtIndex:i]];
            if ([str isEqualToString:@"B1"]) {
                [aMutableArray replaceObjectAtIndex:i withObject:@"B2"];
          }
    }

I maked sure that the B1 element does exist in the array.

Will Pragnell · Accepted Answer · 2012-02-17 14:32:48Z

1

What is happening to your NSMuatbleArray before you get into the for loop?

Is it a property? If so, what is the property declaration? Did you use copy?

If you implement a property like this:

@property (nonatomic, copy) NSMutableArray *myArray;

...then you can run into problems like this because the synthesized setter sends copy to the array, which results in an immutable copy. If this is the case, you need to implement your own setter that calls mutableCopy on the array (or just use retain instead and design your code a little differently).

EDIT:

Based on your comments below and the updated code, I'm sure the problem must be something to do with the array on the app delegate not being mutable.

Try this:

NSMutableArray *mutableThemeseChoosed = [NSMutableArray arrayWithArray:myAppDelegate.themesChoosed];

edited Feb 17, 2012 at 14:32

answered Feb 17, 2012 at 13:43

Will Pragnell

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7 Comments

Luca Over a year ago

I didn't implement a property for that array, i just define it when i need: NSMutableArray *aMutableArray=anotherMutableArray;, should i property it? i am using the ARC.

Will Pragnell Over a year ago

There's no reason that you should need a property for this to work. Have you tried the above with a new muableArray that isn't from 'anotherMutableArray'?

Will Pragnell Over a year ago

Perhaps if you updated the question with more of your code, we might be able to spot something wrong?

Luca Over a year ago

Unfortunately, that was all my code, it's independent of the other code. my NSMutableArray contain the word B1 which i want to replace it y the word B2

lawicko Over a year ago

@Malek well, your application does not agree with this, so maybe you could show us how do you create this array, and how is it assigned to appDelegate.themesChoosed?

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ggfela · Accepted Answer · 2012-02-17 14:25:12Z

0

I just tried your code and it works fine.

NSMutableArray *aMutableArray = [NSMutableArray arrayWithObjects:[NSString stringWithString:@"A1"],[NSString stringWithString:@"B1"],[NSString stringWithString:@"B2"],[NSString stringWithString:@"A1"],[NSString stringWithString:@"A2"],[NSString stringWithString:@"A1"],[NSString stringWithString:@"A1"], nil];

NSLog(@"%@",aMutableArray);

for (int i=0; i<[aMutableArray count]; i++) {
    NSString *str=[NSString stringWithString:[aMutableArray objectAtIndex:i]];
    if ([str isEqualToString:@"B1"]) {
        [aMutableArray replaceObjectAtIndex:i withObject:@"B2"];
    }
}

NSLog(@"%@",aMutableArray);

answered Feb 17, 2012 at 14:25

ggfela

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Comments

tilo · Accepted Answer · 2012-02-17 14:28:38Z

0

Your problem is - as the error tells - that your mutable array is a NSArray (which is not mutable)

What you get out of myAppDelegate.themesChoosed; is likely a NSArray. Try the following: NSMutableArray *aMutableArray= [NSMutableArray arrayWithArray:myAppDelegate.themesChoosed];

answered Feb 17, 2012 at 14:28

tilo

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