Crash during UITableView moveRowAtIndexPath method

Question

I have an array of strings which i am already showing in my uitableview.

When edit is enabled for my uitableview, I am trying to move a string from say 4th row to 3rd row and i get EXC_BAD_ACCESS in the insert object at index part of my code when i debug this..

[myStringsArray insertObject:name atIndex:toIndexPath.row]; 

However if i do not debug and just build and run, i get to print the following line, and then it crashes without seeing EXC_BAD_ACCESS in my console.

NSLog(@"re-ordered myStringsArray array");

Here is my all code for the moveRowAtIndexPath method:

// Override to support rearranging the table view.
- (void)tableView:(UITableView *)tableView moveRowAtIndexPath:(NSIndexPath *)fromIndexPath toIndexPath:(NSIndexPath *)toIndexPath {
    NSArray *paths = NSSearchPathForDirectoriesInDomains( NSDocumentDirectory, NSUserDomainMask, YES); 
    NSString *documentsDirectoryPath = [paths objectAtIndex:0]; 
    NSString *path = [documentsDirectoryPath stringByAppendingPathComponent:@"MyStrings.plist"]; 

    //re-order array
    NSString *name = [myStringsArray objectAtIndex:fromIndexPath.row];
    [myStringsArray removeObjectAtIndex:fromIndexPath.row];
    [myStringsArray insertObject:name atIndex:toIndexPath.row];

    NSLog(@"re-ordered myStringsArray array");
    if([myStringsArray writeToFile:path atomically: YES]){NSLog(@"write succesful");}
    else {NSLog(@"write failed");}

    [myTable reloadData];
}

Any ideas why it thinks that i'm trying to access something that's not there?

Correct me if I am wrong but my mutable array is already allocated and if the remove method worked, why wouldn't the insert method work?

Thank you

Answer 1

When you remove object from array it gets released so there's a good chance that its retain count goes to 0 and it gets deallocated. To avoid premature deallocation you can retain and release your object:

NSString *name = [[myStringsArray objectAtIndex:fromIndexPath.row] retain];
[myStringsArray removeObjectAtIndex:fromIndexPath.row];
[myStringsArray insertObject:name atIndex:toIndexPath.row];
[name release];

Or better use built-in NSMutableArray method for swapping objects you found yourself:

[myStringsArray exchangeObjectAtIndex:fromIndexPath.row withObjectAtIndex:toIndexPath.row];