子类化NSWindow:
- (void)awakeFromNib
{
[selfsetStyleMask:NSBorderlessWindowMask];
[selfsetAcceptsMouseMovedEvents:YES];
[selfsetMovableByWindowBackground:YES];
[selfsetLevel:NSNormalWindowLevel];
[self setOpaque:NO];
[selfsetBackgroundColor:[NSColorclearColor]];
}
- (BOOL) canBecomeKeyWindow { return YES; }
- (BOOL) canBecomeMainWindow { return YES; }
- (BOOL) acceptsFirstResponder { return YES; }
- (BOOL) becomeFirstResponder { return YES; }
- (BOOL) resignFirstResponder { return YES; }