How can I remove all NSTableColumns from an NSTableView?

Question

I am trying to implement a method to clear the NSTableView of all items AND columns. But I get a crash when I try to implement the following:

- (void)clearResultData
{
    [resultArray removeAllObjects];
    NSArray *tableCols = [resultTableView tableColumns];
    if ([tableCols count] > 0)
    {
        id object;
        NSEnumerator *e = [tableCols objectEnumerator];
        while (object = [e nextObject])
        {
            NSTableColumn *col = (NSTableColumn*)object;
            [resultTableView removeTableColumn:col];
        }
    }
    [resultTableView reloadData];
}

Answer 1

Well, if it's any help you can remove all the columns like this:

- (void)removeAllColumns
{
    while([[tableView tableColumns] count] > 0) {
        [tableView removeTableColumn:[[tableView tableColumns] lastObject]];
    }
}

Answer 2

The NSArray returned by tableColumns is changed by removeTableColumn. Do not assume it is unchanged.

Although it is returned as a non-mutable NSArray, the underlying implementation is being modified and it is not safe to use NSEnumerator with collections that are modified. In the while loop, you are sending a nextObject message to an enumerator whose current object was just deleted -- so bad things can happen!

Here's a more efficient implementation:

NSTableColumn* col;
while ((col = [[tableView tableColumns] lastObject])) {
    [tableView removeTableColumn:col];
}

When there are no columns in the table view: tableColumns returns an empty array, lastObject on an empty array returns nil, col is assigned the value of nil, the condition is false and the while loop finishes.