PopupPanelEx in GWT

import com.google.gwt.user.client.ui.*;
import com.google.gwt.user.client.Event;
import com.google.gwt.event.dom.client.KeyCodes;
import static com.google.gwt.user.client.ui.HasHorizontalAlignment.ALIGN_CENTER;

public class PopupPanelEx extends PopupPanel {
    public PopupPanelEx(String title, Widget widget) {
        super(true, true);
        setAnimationEnabled(true);

        final VerticalPanel panel = new VerticalPanel();
        panel.setHorizontalAlignment(ALIGN_CENTER);
        panel.add(new HTML("<h2>" + title + "</h2>"));
        panel.add(widget);
        setWidget(panel);
    }

    @Override
    protected void onPreviewNativeEvent(Event.NativePreviewEvent event) {
        super.onPreviewNativeEvent(event);
        if (event.getTypeInt() == Event.ONKEYDOWN) {
            final int code = event.getNativeEvent().getKeyCode();
            switch (code) {
                case KeyCodes.KEY_ENTER:
                case KeyCodes.KEY_ESCAPE:
                    hide(); break;
            }
        }
    }
}