Why do I get MouseDown events from a position outside of the control's boundary? - eclipse

Question

I have a Composite containing a number of Text controls. I have attached MouseListeners to each control.
What surprises me is that sometimes, when I click on a control, I get a MouseDown event from its neighbour. The Event position is outside of the control's boundary and I get no event from the other control which I thought I had clicked on.
What can cause this to happen?
SNIPPET
Run. Press Esc to close the MessageBox. Click in field BBBB. Press Esc to close MessageBox. Click in field AAAA. The event is generated from field BBBB.
public class Test
{
public class MyListener implements MouseListener, FocusListener
{
private boolean active;
#Override
public void focusGained(FocusEvent e)
{
System.out.println(e);
message((Text) e.widget, "FocusGained");
}
#Override
public void focusLost(FocusEvent e)
{
System.out.println(e);
}
#Override
public void mouseDoubleClick(MouseEvent e)
{
}
#Override
public void mouseDown(MouseEvent e)
{
System.out.println(e);
}
private void message(final Text t, final String m)
{
if (active == false)
{
active = true;
MessageBox mb = new MessageBox(t.getShell());
mb.setText(m);
mb.setMessage(t.getMessage() + "\n\n" + m);
mb.open();
active = false;
}
}
#Override
public void mouseUp(MouseEvent e)
{
System.out.println(e);
message((Text) e.widget, e.toString());
}
}
private MyListener listener = null;
public static void main(String[] args)
{
Display display = new Display();
Shell shell = new Shell(display);
new Test(shell);
shell.open();
while (!shell.isDisposed())
{
if (!display.readAndDispatch())
display.sleep();
}
display.dispose();
}
public Test(Composite parent)
{
listener = new MyListener();
create(parent);
}
private void create(Composite parent)
{
parent.setLayout(new GridLayout(2, true));
createText(parent, "AAAA");
createText(parent, "BBBB");
parent.layout(true);
}
private Text createText(Composite parent, String message)
{
Text t = new Text(parent, SWT.NONE);
t.setMessage(message);
GridData gd = new GridData(SWT.FILL, SWT.CENTER, true, false);
t.setLayoutData(gd);
t.addFocusListener(listener);
t.addMouseListener(listener);
return t;
}
}

Answer 1

This is indeed strange. When traversing from B to A, the MouseUp event is marked as sent from field B.
If you replace the MessageBox with something non-interrupting i.e. System.out, the mouse event senders are the right ones.
To me, this seems more of a theoretical corner case. Decent applications would not interrupt the users field traversal with a modal window. However, if this is relevant for your, I'd report a bug to SWT.

Answer 2

I managed to get this working by de-coupling the pop-up window from the events. The message method now looks like this:
private void message(final Text t, final String m)
{
//NB active is declared as 'volatile'
if (active == false)
{
active = true;
t.getDisplay().asyncExec(new Runnable()
{
#Override
public void run()
{
MessageBox mb = new MessageBox(t.getShell());
mb.setText(m);
mb.setMessage(t.getMessage() + "\n\n" + m);
mb.open();
active = false;
}
});
}
else
{
System.out.println("Already active: " + t.getMessage());
}
}
This seems to give the events the opportunity to continue uninterrupted by the pop-up window. The pop-up will be activated a short while later. So far it works ok.