GeoMap isn't centring correctly

Question

I have an RCP view with a GeoMap widget inside it. When the view is created, the map is centred on a position.

The problem I'm having is that when GeoMap calls getSize() it is wrong. It is returning (0,0).

I've found one method of fixing this but it required changing code in GeoMap even though I believe the problem is to do with the code in the view. If I change the setCenterPosition method for GeoMap to use the parents client area it works.

View

@PostConstruct
public void createPartControl(final Composite parent) {
    Display.getDefault().asyncExec(() -> setInitialPosition());
}

private void setInitialPosition() {
    widget.setCenterPosition(new PointD(longitude, latitude));
    widget.redraw();
}

GeoMap

public void setCenterPosition(final Point p) {

    // `parent.getClientArea()` instead of `getSize()`
    final Rectangle size = getParent().getClientArea();

    setMapPosition(p.x - (size.width / 2), p.y - (size.height / 2));
}

The problem with this is that I've had to change code in GeoMap to fix a problem that is likely to do with getting the size of the view. The view hasn't had the size set by the time I call to centre the map.

I've also tried adding a resize listener to the view. This wouldn't always produce the same results when getting the size of the GeoMap widget.

parent.addListener(SWT.Resize, new Listener() {
    @Override
    public void handleEvent(final org.eclipse.swt.widgets.Event e) {
        if (firstResize) {
            setInitialPosition();
            firstResize = false;
        }
    }
});

Here mentions that a resize listener should be used, and getClientArea. The problem is that GeoMap doesn't use getClientArea but I don't know if it should be.

Is this a problem with how I'm calling setCenterPosition or a bug in GeoMap?

Update

I've also tried adding a resize listener to the widget.

widget.addListener(SWT.Resize, new Listener() {
    @Override
    public void handleEvent(final org.eclipse.swt.widgets.Event e) {
        if (firstResize) {
            setInitialPosition();
            firstResize = false;
        }
    }
});

For some reason the size the widget gets is too small. It is getting a size of (615, 279) when it should be (768, 388). By adding a button to call setCenterPosition again it gets the correct size of (768, 388).

I can fix this if I add it inside an async block but this seems more like a workaround than an actual fix.

widget.addListener(SWT.Resize, new Listener() {
    @Override
    public void handleEvent(final org.eclipse.swt.widgets.Event e) {
        if (firstResize) {
            Display.getDefault().asyncExec(() -> {
                setInitialPosition();
                firstResize = false;
            });
        }
    }
});