Dialog sheet

I have two xibs MainMenu and dialogSheet

when opens dialog Sheets the focus still stay at the MainWindow.
dialogSheet has a button for close which works, but the other controls can't get on focus.

Code:

- (IBAction) showSheet:(NSWindow*)window
{
	
    
        if (!_clientsDialog)
            [NSBundle loadNibNamed: @"clientsDialog" owner: self];
            [NSApp beginSheet:self.clientsDialog
               modalForWindow:[[NSApp delegate]window]
                modalDelegate: self
               didEndSelector: NULL
                  contextInfo: NULL];
    
    
}