crash while removing objects from NSMutableArray

Question

In my iphone project (ARC enabled) i have a nsmuatble array which contains some 5 managed objects (which are retrieved from core data ) and in some scenario i need to remove all the objects from that nsmutablearray

i have used following methods to remove objects but its crashing in both the cases with the crash log -[__NSArrayI removeObject:]: unrecognized selector sent to instance 0xa391640

if (surveys && [surveys count]>0)
        {

            [surveys removeAllObjects];
            surveys = [[NSMutableArray alloc]init];
        }

and also i tried

if (surveys && [surveys count]>0)
        {
            for(Survey *obj_Survey in surveys)
            {
                [surveys removeObject:obj_Survey];
            }

            surveys = [[NSMutableArray alloc]init];
        }

can any one tell me how do i empty that array,, any suggestions would be appreciated, thanx in advance

Answer 1

The answer is very simple.

For First case.
Check the part where you have initialized your array, and check if somewhere through your code, if you have assigned an NSArray to your NSMutableArray object.

For second case.
You cannot remove objects from the array while you are enumerating through it. This will result in a crash saying array has mutated while enumerating

Answer 2

This:

[__NSArrayI removeObject:] : unrecognized selector sent to instance 0xa391640

indicates that your array "surveys" is NSArray (not-mutable). Are you sure you have initialized it properly? If you do it by an assignment like this

NSMutableArray* surveys = [someManagedObjectContext executeFetchRequest:request]

an array "surveys" will be of type NSArray because Core Data fetch requests return NSArrays.

Answer 3

The error message says it all,

[__NSArrayI removeObject:]: unrecognized selector

__NSArrayI is a code-word for an immutable array (NSArray), That means your surveys object is not NSMutablArray, but NSArray.

You cannot add or remove objects from NSArray.

Check your code. You have assigned NSArray to surveys or you have reinitialized it as NSArray.

Answer 4

Remove all the things that you are doing and simply do like this

 [surveys removeAllObjects];

As from the error that you are getting so maybe that Array is not NSmutableArray just normal array so thats why you can not remove object from It and you try to do so and app got crash

check where you have initialised it if it is Mutable or not

so as I said remove all that thing and use simple removeAllObject

Answer 5

From the exception it's very evident that at some point you are assigning an immutable instance to your mutable array. From the comments I could make out that you were sorting surveys and sorted array was returning immutable array. Type casting will not do good for getting mutableCopy of an immutable object.

NSArray *sortDescriptors = [[NSArray alloc] initWithObjects:sortDescriptor1,nil]; 
surveys = (NSMutableArray *) [[[NSMutableArray alloc]initWithArray:surveys ] sortedArrayUsingDescriptors:sortDescriptors];

Instead of it use

[surveys sortUsingDescriptors: @[sortDescriptor1]];

Answer 6

You might have initialised with Immutable Array. Use the following Code:

NSMutableArray *newArray = [NSMutableArray arrayWithArray: oldArray];