gistfile1.m

- (void)keyDown:(NSEvent *)theEvent {
    unsigned short key = [theEvent keyCode];
    
    BOOL up;
    if (key == 38) up = NO;
    else if (key == 40) up = YES;
    else return [super keyDown:theEvent];
    BOOL down = !up;
    
    NSInteger index = [self selectedRow];
    NSInteger total = [self numberOfRows];
    NSInteger desiredChange;
    if (down) desiredChange = 1;
    if (up) desiredChange = -1;
    NSInteger desired = index + desiredChange;
    
    if (index < 0) index = 0;
    else if (index > total) index = total;
    
    while (desired >= 0 && desired <= total) {
        if ([[self delegate] outlineView:self shouldSelectItem:[self itemAtRow:desired]]) break;
        desired += desiredChange;
    }
        
    [self selectRowIndexes:[NSIndexSet indexSetWithIndex:desired] byExtendingSelection:NO];
}