gistfile1.java

/**
 * Simple panel that wraps a GWT simple panel to be replaced by the widgetToAttach we set while updating the references.
 * <p/>
 * The result of this will be to have a better, cleaner, dom.
 */
public class ReplacePanel implements IsWidget, HasOneWidget {
    static class WrongParentTypeException extends RuntimeException {
        public WrongParentTypeException(String message) {
            super(message);
        }
    }

    private IsWidget widget;

    public ReplacePanel() {
        SimplePanel simplePanel = new com.google.gwt.user.client.ui.SimplePanel();
        widget = simplePanel;

        simplePanel.addAttachHandler(new Handler() {
            @Override
            public void onAttachOrDetach(AttachEvent event) {
                Widget parentAsWidget = getParent();

                if (!(parentAsWidget instanceof HTMLPanel)) {
                    throw new WrongParentTypeException("The parent of ReplacePanel must be of type HTMLPanel");
                }
            }
        });
    }

    @Override
    public Widget asWidget() {
        return widget.asWidget();
    }

    @Override
    public Widget getWidget() {
        return widget.asWidget();
    }

    @Override
    public void setWidget(Widget widgetToAttach) {
        Widget parentAsWidget = getParent();

        if (parentAsWidget != null && parentAsWidget instanceof HTMLPanel) {
            HTMLPanel parent = (HTMLPanel) parentAsWidget;

            parent.addAndReplaceElement(widgetToAttach, widget.asWidget().getElement());

            widget = widgetToAttach;
        }
    }

    @Override
    public void setWidget(IsWidget widget) {
        setWidget(widget.asWidget());
    }

    private Widget getParent() {
        return widget.asWidget().getParent();
    }
}