How to copy correctly a NSMutableArray?

Question

I want to copy a NSMutableArray with the code below :

SectionArray *newSectionArray = [[SectionArray alloc] init];    
NSMutableArray *itemsCopy = [self.sections mutableCopy];
newSectionArray.sections = [[NSMutableArray alloc] initWithArray:itemsCopy copyItems:YES];

But I have an error when I try to set an object in this new array :

[[self.sections objectAtIndex:intSection] replaceObjectAtIndex:intRow withObject:object];

[__NSArrayI replaceObjectAtIndex:withObject:]: unrecognized selector sent to instance 0x7191720

I also tried :

SectionArray *newSectionArray = [[SectionArray alloc] init];    
newSectionArray.sections = [[[NSMutableArray alloc] initWithArray:itemsCopy copyItems:YES] mutableCopy];

My SectionArray class :

@implementation SectionArray

@synthesize sections;
@synthesize value;

- initWithSectionsForWayWithX:(int)intSections andY:(int)intRow {
    NSUInteger i;
    NSUInteger j;

    if ((self = [self init])) {
        sections = [[NSMutableArray alloc] initWithCapacity:intSections];
        for (i=0; i < intSections; i++) {
            NSMutableArray *a = [NSMutableArray arrayWithCapacity:intRow];
            for (j=0; j < intRow; j++) {
                Node * node = [[Node alloc] initNodeWithX:i  andY:j andValeur:0];
                [a insertObject:node atIndex:j];
            }
            [sections addObject:a];
        }
    }
    return self;
}

- (void)setObjectForNode:(Node *)object andX:(int)intSection andY:(int)intRow {

    [[sections objectAtIndex:intSection] replaceObjectAtIndex:intRow withObject:object];
}

- (SectionArray *) copy {
    ...
}

@end

Answer 1

If I see it correctly then sections is a mutable array, but its elements

[sections objectAtIndex:intSection]

are immutable arrays , so you get the exception at

[[sections objectAtIndex:intSection] replaceObjectAtIndex:intRow withObject:object];

The reason is that you copy the items here ( copyItems:YES ):

newSectionArray.sections = [[NSMutableArray alloc] initWithArray:itemsCopy copyItems:YES];

so even if itemsCopy is an array of mutable arrays, the copies of these elements are immutable.

Added: For a "nested mutable copy" of your nested array you could procede as follows:

SectionArray *newSectionArray = [[SectionArray alloc] init];
newSectionArray.sections = [[NSMutableArray alloc] init];
for (NSUInteger i=0; i < [sections count]; i++) {
    NSMutableArray *a = [[sections objectAtIndex:i] mutableCopy];
    [newSectionArray.sections addObject:a];
}