GWT event prevent default not working in Java

Question

I'm new to GWT and I need to get a right click working. The doco I've read suggests that I need to override the onBrowserEvent() method. I'm just experimenting at this stage. the event is processed and my pop-up appears. However, as soon as I close the pop-up, the usual browser drop down menu appears (with options like "Bookmark this page" and such).

I'm using IceWeasel 24.5.0 (FireFox clone for Debian) and, obviously, Debian (wheezy).

Here's the relevant code:

public ActivityTextCell() {
    super(BrowserEvents.MOUSEDOWN, BrowserEvents.MOUSEUP);
}

@Override
public void onBrowserEvent(
        com.google.gwt.cell.client.Cell.Context context,
        Element parent, 
        ActivityDTO value, 
        NativeEvent event,
        ValueUpdater<ActivityDTO> valueUpdater) {

    super.onBrowserEvent(context, parent, value, event, valueUpdater);
    event.preventDefault();
    event.stopPropagation();
    if (event.getType().equals(BrowserEvents.MOUSEUP)) {
        Window.alert("mouse up event");

    }
    else {

        switch ( event.getButton()){
        case NativeEvent.BUTTON_RIGHT:
            Window.alert("right mouseclick");
            break;
        case NativeEvent.BUTTON_LEFT:
            Window.alert("left mouseclick");
            break;
        case NativeEvent.BUTTON_MIDDLE:
        default:
            break; // Do nothing
        }
    }

The class ActivityTextCell extends AbstractCell.

So what am I missing? How do I stop the browser from reaticng to the mouse click?

Achim Schmitz Achim Schmitz · Accepted Answer · 2014-08-13T20:05:59

Well it certainly wasn't a matter of a few minutes (as can be seen by the fact that it has taken me a week to get back to this), but I have a solution. I tried reversing the order of the the event.preventDefault() and super.onBrowserEvent() but it didn't really help.

I tried a little experiment on a normal web page. It turns out, that the MOUSEDOWN event doesn't do anything in that context and the usual browser selection menu appears on the MOUSEUP. So the if/else logic sort of fell by the wayside.

What did the trick is to include the following in the top level GUI class immediately after adding the main page:

RootLayoutPanel.get().addDomHandler(new ContextMenuHandler() {

    @Override
    public void onContextMenu(ContextMenuEvent event) {
        event.preventDefault();
        event.stopPropagation();
    }
}, ContextMenuEvent.getType());

This has the additional benefit (for my purposes, at least) of preventing the Browser from reacting to a right click anywhere in the application view.

As an aside: The purpose of preventing the default action is to stop the Browser doing its own thing Stopping propagation is possibly not required, but I left it in anyway (propagation goes fro the node up to the root, not the other way around). The purpose of overridinging onBrowserEvent() is to enable your own application to handel that event. The use of super.onBrowserEvent() is to allow the event to be handled by your code in the first place. I've given the relevant reference in my previous comment. The book "GWT in Action" is well worth a read if you're likely to be doing a lot of GWT coding.

GWT event prevent default not working in Java

2 Answers