Question

I’m trying to remove last two value from array. So, i used to do below code –

-(void)connectionDidFinishLoading:(NSURLConnection *)connection
{

    NSString *resMsg = [[NSString alloc] initWithBytes: [webData mutableBytes] length:[webData length] encoding:NSUTF8StringEncoding];
    NSData *responseData = [resMsg dataUsingEncoding:NSUTF8StringEncoding];

    NSError *error = nil;

    if (responseData != nil) 
    {

        array = [NSJSONSerialization JSONObjectWithData:responseData options:0 error:&error];

        if([array count] == 2) {

        }else
        {
             int k = [self.array count] -2 ;
             int l = [self.array count] -1 ;

             [self.array removeObjectAtIndex:l];
             [self.array removeObjectAtIndex:k];

             [gridTable reloadData];
             [tblProducts reloadData];
         }

    }

}

But, its giving below exception –

Terminating app due to uncaught exception ‘NSInternalInconsistencyException’, reason: ‘-[__NSCFArray removeObjectAtIndex:]: mutating method sent to immutable object’

I don’t know why this happened? I’ve already used this method in another viewController class too. It was working fine there. But, here its giving exception.

Answer 1

The object returned from [NSJSONSerialization JSONObjectWithData:responseData options:0 error:&error]; will return an autoreleased NSArray. If you want to make it mutable, you’ll have to call NSMutableArray *mutableArray = [array mutableCopy];

Your other option here is instead of putting in a 0 for your options: parameter, put NSJSONReadingMutableContainers. This will solve your problem without creating an extra object.

EDIT

In order to fix your new problem:

NSMutableArray *newData = [NSJSONSerialization JSONObjectWithData:responseData options:NSJSONReadingMutableContainers error:&error];
//Here, modify the new array.  Remove your last two items. Then..
[newData addObjectsFromArray:array];
array = newData;

As a side note, this may cause you to have your array objects in a different order than you expect. You may choose to call this…

NSSortDescriptor *sort = [NSSortDescriptor sortDescriptorWithKey:@"key" ascending:YES];
array = [newData sortedArrayUsingDescriptors:[NSArray arrayWithObject:sort]];