replace object in mutable array

Question

This should be rather easy and probably I'm just missing a small thing: I have an array of images called defaultImages

NSMutableArray *defaultLetters;

then I add the letters needed (array length then is 42)

later I'm trying to replace one of the images in the array with another image. Like this:

[defaultLetters replaceObjectAtIndex:0 withObject:croppedPhoto];

but I'm getting an error saying: "-[__NSArrayI replaceObjectAtIndex:withObject:]: unrecognized selector sent to instance 0x180ae190" is there a step I'm missing?

please show us, how you assign something to defaultLetters — vikingosegundo
– vikingosegundo, Commented Oct 25, 2013 at 12:55

TamilKing · Accepted Answer · 2013-10-25 13:26:36Z

8

I think you assign value like this

defaultLetters = anotherMutableArray;

If you do like this, then please replace as below..

defaultLetters = [anotherMutableArray mutableCopy];

Ater you can replace object in that array

[defaultLetters replaceObjectAtIndex:0 withObject:croppedPhoto];

Try this..Because if you directly assign you can't insert or remove.

edited Oct 25, 2013 at 13:26

answered Oct 25, 2013 at 12:56

TamilKing

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Community · Accepted Answer · 2017-05-23 10:30:44Z

7

You assigned a NSArray object to defaultLetters, not a NSMutableArray.

__NSArrayI is a private Subclass of NSArray. The I stands for immutable.

see What is __NSArrayI and __NSArrayM? How to convert to NSArray?

if you can't tell for sure, if it is an NSArray or an NSMutableArray you are assigning, you can always test.

if(![defaultLetters respondsToSelector:@selector(replaceObjectAtIndex:withObject:)]){
    defaultLetters = [defaultLetters mutableCopy];
}

But this might indicate an architectural issue within your code, as you should know for certain what objects you are dealing with.

edited May 23, 2017 at 10:30

CommunityBot

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answered Oct 25, 2013 at 12:51

vikingosegundo

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