Getting notified when an NSView comes to the foreground

Question

I have a NSTableView inside the second tab of a NSTabView. The table uses some custom event code that takes care of buttons in the table being clicked are recognised. The problem is that even if I have the first or third tab of the tab view open (i.e. table view is not visible), these events are being intercepted (so if I have buttons on 1./3. tab they don't work).

To solve this I added a flag to my custom table view class to only execute the custom event code when the flag is true and if not just return the original event.

Now I'm wondering how do I tell if the table view is in the front (i.e. tab no. 2 is open)? Is there any elegant way to check for this or do I need to get this from the tab bar directly?

In case it matters, here's my custom table code...

class ButtonTableView : NSTableView
{
    var isAtForeground:Bool = false;

    override init(frame frameRect:NSRect) {
        super.init(frame: frameRect);
    }

    required init?(coder:NSCoder) {
        super.init(coder: coder);
        addEventInterception();
    }

    /// Get the row number (if any) that coincides with a specific point - where the point is in window coordinates.
    func rowContainingWindowPoint(windowPoint:CGPoint) -> Int? {
        var rowNum:Int?;
        var tableRectInWindowCoords = convertRect(bounds, toView: nil);
        if (CGRectContainsPoint(tableRectInWindowCoords, windowPoint))
        {
            let tabPt = convertPoint(windowPoint, fromView: nil);
            let indexOfClickedRow = rowAtPoint(tabPt);
            if (indexOfClickedRow > -1 && indexOfClickedRow < numberOfRows)
            {
                rowNum = indexOfClickedRow;
            }
        }
        return rowNum;
    }

    func addEventInterception() {
        NSEvent.addLocalMonitorForEventsMatchingMask(.LeftMouseDownMask, handler:
        {
            (theEvent) -> NSEvent! in

            /* Don't bother if the table view is not in the foreground! */
            if (!self.isAtForeground) { return theEvent; }

            var e:NSEvent? = theEvent;
            let p:NSPoint = theEvent.locationInWindow;

            /* Did the mouse-down event take place on a row in the table? */
            if let row = self.rowContainingWindowPoint(p)
            {
                let localPoint = self.convertPoint(p, fromView: nil);

                /* Get the column index that was clicked in. */
                let col = self.columnAtPoint(localPoint);

                /* Get the table cell view on which the mouse down event took place. */
                let tcv = self.viewAtColumn(col, row: row, makeIfNecessary: false) as! NSTableCellView;

                /* Did the click occur on the table view? */
                let tableBoundsInWindowCoords:NSRect = self.convertRect(self.bounds, toView: nil);
                if (CGRectContainsPoint(tableBoundsInWindowCoords, p))
                {
                    /* If clicked anywhere in the table cell view, only allow button areas to pass. */
                    /* subView is the NSTableCellView's last subview. */
                    var subView = tcv.subviews.last! as! NSView;
                    let subViewBoundsInWindowCoords:NSRect = subView.convertRect(subView.bounds, toView: nil);
                    /* Did the click occur on the subview part of the view? */
                    if (CGRectContainsPoint(subViewBoundsInWindowCoords, p))
                    {
                        /* Only allow button subviews to be clicked. */
                        if let button = subView as? NSButton
                        {
                            // Create a modified event, where the <location> property has been
                            // altered so that it looks like the click took place in the
                            // NSTableCellView itself.
                            let newLocation = tcv.convertPoint(tcv.bounds.origin, toView: nil);
                            e = theEvent.cloneEventButUseAdjustedWindowLocation(newLocation);
                            return e;
                        }
                    }
                    /* If we've reched here, the user clicked anywhere on the table but not one of the buttons. */
                    return nil;
                }
            }
            return e;
        });
    }
}