using copy in nested NSMutableArrays gives immutable objects?

• Randy using copy in nested NSMutableArrays gives immutable objects? Nov 16 2008, 06:56
  In my program I have nested NSMutableArrays, i.e., each element in a
  root NSMutableArray is a NSMutableArray.
  
  When I try to grab one of the element NSMutableArrays ......
  NSMutableArray *copyOfCurrent = (NSMutableArray *) [[walkerArray
  objectAtIndex:lastNodeInCurrent] copy];//walkerArray is another
  NSMutableArray
  
  As soon as I try to alter (insert an element for example)
  copyOfCurrent I get a "NSInternalInconsistencyException" with the
  message "mutating method sent to immutable object".  It looks like
  either the objectAtIndex or the copy method is providing something
  immutable, not an NSMutableArray.
  
  Any idea why that might be happening?
  
  I was able to get around the problem by creating a new NSMutableArray
  and loading into it the contents of the immutable one like ..
  
  NSMutableArray *copyOfCurrent = (NSMutableArray *) [[walkerArray
  objectAtIndex:lastNodeInCurrent] copy];
  NSMutableArray *fixError = [[NSMutableArray alloc] init];
  int k;
  for (k = 0; k < [copyOfCurrent count]; k++)
  {
  fixError[k] = copyOfCurrent[k];
  }
  
  But that seems hokey and I would like to understand the cause of the
  original issue.
  
  Thanks;
  
  Randy
• Nathan Kinsinger Re: using copy in nested NSMutableArrays gives immutable objects? Nov 16 2008, 07:11
  On Nov 15, 2008, at 10:56 PM, Randy wrote:
  
  

  > In my program I have nested NSMutableArrays, i.e., each element in a
  > root NSMutableArray is a NSMutableArray.
  >
  > When I try to grab one of the element NSMutableArrays ......
  > NSMutableArray *copyOfCurrent = (NSMutableArray *) [[walkerArray
  > objectAtIndex:lastNodeInCurrent] copy];//walkerArray is another
  > NSMutableArray
  >
  > As soon as I try to alter (insert an element for example)
  > copyOfCurrent I get a "NSInternalInconsistencyException" with the
  > message "mutating method sent to immutable object".  It looks like
  > either the objectAtIndex or the copy method is providing something
  > immutable, not an NSMutableArray.
  >
  > Any idea why that might be happening?
  >
  > I was able to get around the problem by creating a new
  > NSMutableArray and loading into it the contents of the immutable one
  > like ..
  >
  > NSMutableArray *copyOfCurrent = (NSMutableArray *) [[walkerArray
  > objectAtIndex:lastNodeInCurrent] copy];
  > NSMutableArray *fixError = [[NSMutableArray alloc] init];
  > int k;
  > for (k = 0; k < [copyOfCurrent count]; k++)
  > {
  > fixError[k] = copyOfCurrent[k];
  > }
  >
  > But that seems hokey and I would like to understand the cause of the
  > original issue.
  >
  > Thanks;
  >
  > Randy
  

  
  -copy returns an immutable object (as you found out), -mutableCopy is
  what you want.
  
  --Nathan