gistfile1.txt

@implementation MyDel
- (void)comboBoxSelectionDidChange:(NSNotification *)notification
{
    NSLog (@"Did Change");
}
- (void)comboBoxSelectionIsChanging:(NSNotification *)notification
{
    NSLog (@"Is Changing");
}
@end

@implementation ViewController
            
- (void)viewDidLoad {
    [super viewDidLoad];
    NSComboBox * b = [[NSComboBox alloc] initWithFrame:NSMakeRect(0, 0, 200, 25)];
    [b addItemsWithObjectValues:@[@"1", @"2", @"3"]];
    b.delegate = [[MyDel alloc]init];
    [[self view]addSubview:b];