To summarize, support for a new component requires adding special support for this component into GWT Designer. Assume I have a custom component which I want it to act like a VerticalPanel but which infact is type composite :
public class CustomPanel extends Composite implements HasWidgets{
private VerticalPanel panel = new VerticalPanel();
public CustomPanel() {
initWidget(panel);
}
@Override
public void add(Widget w) {panel.add(w);}
@Override
public void clear() {panel.clear();}
@Override
public Iterator<Widget> iterator() {return panel.iterator();}
@Override
public boolean remove(Widget w) {return panel.remove(w);}
}
This will work as a VerticalPanel, but when you are looking from the Designers perspective this still is a Composite. As a result you can not drop widgets inside it. In the simplest case, what you should do to make it designer friendly is to create a CustomPanel.wbp-component.xml in the same package of CustomPanel following given name convention. A simple one to give flow like widget adding behaviour would be,
<?xml version="1.0" encoding="UTF-8"?>
<component xmlns="http://www.eclipse.org/wb/WBPComponent">
<description>This is a simple Composite acting like VerticalPanel</description>
<!-- CREATION -->
<creation>
<source><![CDATA[new org.test.client.CustomPanel()]]></source>
</creation>
<parameters>
<parameter name="flowContainer">true</parameter>
<parameter name="flowContainer.horizontal">false</parameter>
<parameter name="flowContainer.association">%parent%.add(%child%)</parameter>
</parameters>
</component>
After adding this step your composite should be treated like a vertical panel (dropping widgets inside support) by the gwt designer as well. When this XML alone is not enough, meaning you need some behavior more of a complex nature, you need to start writing java model classes that defines custom behaviour of your component to Designer and reference it in your component xml using <model> tag. In this case you need to write a plugin to host your models and policies.
Here are the references for this summary and useful links:
