Fire event when switching stacks of StackLayoutPanel in GWT 2.0

I'm trying to catch an event, when I switch the stacks of a StackLayoutPanel in GWT 2.0.

The biggest problem is that I don't know which 开发者_开发知识库event gets fired and there seems to be no documentation, I have added a ChangeHandler with addDomHandler() but that hasn't worked.

Unfortunately the StackLayoutPanel doesn't implement the getSelectedIndex()-function so I can't just use an ClickEvent and then check if the selected index has changed.

Is my only solution to use the StackPanel or is there a way to get this to work with the StackLayoutPanel?

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I believe in GWT 2.0.3 StackLayoutPanel has method addSelectionHandler. Fired event is SelectionEvent and event.getSelectedItem() returns corresponding stack header id.

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What I did, after some experiments: use a Label as the widget of the header with 100% width and then add a ClickEvent handler attached. Every time the ClickEvent arrives, it means the user clicked the header, so the panel will be visible... Not very nice, but it worked. I tried to wrap the header widget using a ClickWrapper (take a look to the StackLayoutPanel source code), but it didn't worked, I dont know exactly why...

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I did it this way

public class StackComponent extends StackLayoutPanel implements HasChangeHandlers {

public StackComponent(Unit unit) {
    super(unit);
}

@Override
public void showWidget(Widget widget) {
    super.showWidget(widget);
    fireEvent(new StackChangeEvent(widget));

}

@Override
public HandlerRegistration addChangeHandler(ChangeHandler handler) {
    return addDomHandler(handler, ChangeEvent.getType());
}

}

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This worked form me:

private int selectedIndex = 0;

public Main() {
    initWidget(ourUiBinder.createAndBindUi(this));

    navigatorStackPanel.add(yourWidgetOne, "Title one");

    navigatorStackPanel.add(yourWidgetTwo, "Title two");

    navigatorStackPanel.addHandler(new ClickHandler() {
        @Override
        public void onClick(ClickEvent event) {
            if (navigatorStackPanel.getSelectedIndex() != selectedIndex) {
                selectedIndex = navigatorStackPanel.getSelectedIndex();
                if (selectedIndex == 0)
                    do something one;
                else
                    do something two;
                GWT.log(" Changed");
            }
        }
    }, ClickEvent.getType());
}