SWT event propagation

Question

I'm trying to detect click events on a Composite control that contains a number of other composites. I tried:

topComposite.addMouseListener(new MouseListener() {
        ...
        @Override
        public void mouseUp(MouseEvent arg0) {
            logger.info("HERE");
        });
});

But the event never fires. I assumed that when a mouse event occurred on a child it would propagate up the chain but that doesn't happen. How do I do this?

Underprop

Answer 1

In SWT, the general rule is that events do not propagate. The main exception to this, is the propagation of traverse events - which is pretty complicated to describe.

The easy answer to your problem is that you must add the listener to all the children of you Composite - recursively!

E.g. like this

public void createPartControl(Composite parent) {
    // Create view...

    final MouseListener ma = new MouseAdapter() {
        @Override
        public void mouseDown(MouseEvent e) {
            System.out.println("down in " + e.widget);
        }
    };
    addMouseListener(parent, ma);
}

private void addMouseListener(Control c, MouseListener ma) {
    c.addMouseListener(ma);
    if (c instanceof Composite) {
        for (final Control cc : ((Composite) c).getChildren()) {
            addMouseListener(cc, ma);
        }
    }
}

The clicked-upon widget is found in e.widget as seen above. An important issue is to remember to do this again if you add more Controls later.

Dermatosis

alternatively, if you do not want t add so many listeners - you can use a workaround. Capture ALL occured MouseEvents by composite.getDisplay().addFilter(SWT.KeyDown, new Listener() {...} and somehow pick the relevant events. – Acerbate

@Acerbate This is indeed possible as well, but be careful to deregister the listener again :-) – Dermatosis