The reason you are seeing the data populated in multiple columns is you are not differentiating what values go in what columns.
You should think of each item in your array as a row in your table view. If you wish to display different values in columns of that row you need a way to store those different values in the data source object. This can be done by using a concrete model object class that has multiple properties defined or by using a NSDictionary with different keys with their corresponding values.
For adding a row:
-(IBAction)addTask:(id)sender
{
NSMutableDictionary *newRow = [NSMutableDictionary dictionary];
[newRow setObject:@"Hello World" forKey:@"salutation"];
[self.data addObject:newRow];
[self.tableView reloadData];
}
So for the display code:
- (id)tableView:(NSTableView *)aTableView objectValueForTableColumn:(NSTableColumn *)aTableColumn row:(NSInteger)rowIndex
{
NSDictionary *row = [self.data objectAtIndex:rowIndex];
NSString *columnIdentifier = [aTableColumn identifier];
return [row objectForKey:columnIdentifier];
}
You'll notice we are using the column identifier here. Normally you set this value in Interface Builder on the table column. In the case above the identifier needs to be the same as the key in the dictionary for which you wish to display information.
Finally allowing the user to set a value of a column in the table view:
-(void)tableView:(NSTableView *)aTableView setObjectValue:(id)anObject forTableColumn:(NSTableColumn *)aTableColumn row:(NSInteger) rowIndex
{
NSDictionary *row = [self.data objectAtIndex:rowIndex];
NSString *columnIdentifier = [aTableColumn identifier];
[row setValue:anObject forKey:columnIdentifier];
}