Allow views in childWindow to become key without l

I added a childWindow of a custom subclass of NSWindow to a parentWindow (also a custom subclass of NSWindow). The childWindow has the NSBorderlessWindowMask and canBecomeKeyWindow: is overridden to return YES and canBecomeMainWindow: to return NO.

The childWindow is set to resize with the parentWindow. So I want to create the illusion that the views of the childWindow are part of the parentWindow. The main idea is to arrange the document windows created by the document-based application within a main window to provide a tabbed interface (just like in a browser) to switch between the documents.

My problem is that whenever I click in one of the views of the childWindow, the parentWindow (the main window) looses focus and the traffic light buttons are getting greyed out. This is obviously contrary to what I want to achieve.

I found this answer: Make NSView in NSPanel first responder without key window status

But even if I override isKeyWindow: (of the main window) to always return YES, the title bar gets greyed out nonetheless when I click into the childWindow.

I also tried to follow this advice: http://www.cocoabuilder.com/archive/cocoa/143945-non-focused-child-window.html

But I'm not sure what "include the child window in its responder chain just ahead of its nextResponder" means. With canBecomeKeyWindow: to return NO (for the childWindow), the views within the child never can become key and are always greyed out.

Any clue what I am doing wrong?

One addition: Is it possible to make the views in the childWindow FirstResponder without giving the childWindow key-status?

I got this working by mimicking the behaviour of NSPopover. On investigation I found that a popover (which uses a private NSPanel subclass "_NSPopoverWindow") believed it was the key & main window, even though it is not the window returned from [NSApp keyWindow].

Create your own custom NSPanel subclass, attach it to the parent window, and then override the following methods as so:

- (BOOL)isKeyWindow {
    return YES;
}

- (BOOL)isMainWindow {
    return YES;
}

- (BOOL)canBecomeKeyWindow {
    return YES;
}

- (BOOL)canBecomeMainWindow {
    return YES;
}

- (void)makeKeyWindow {
    [super makeKeyWindow];
    [self.parentWindow makeKeyWindow];
}
- (void)makeMainWindow {
    [super makeMainWindow];
    [self.parentWindow makeMainWindow];
}
- (void)becomeKeyWindow {
    [super becomeKeyWindow];
}

- (void)becomeMainWindow {
    [super becomeMainWindow];
    [self.parentWindow becomeMainWindow];
}

- (void)resignMainWindow {

}
- (void)resignKeyWindow {

}