a simple UIBinder widget contains an html element with an id. AFTER calling initWidget(uiBinder.createAndBindUi(this)); document.getElementById() will return null. Only in an attach event listener I can retrieve the element by id. In the example I instantiate the widget directly from the entry point using RootPanel.get().add(new MainPanel())

gistfile1.txt

package org.sgx.raphael4gwt.raphy.test.app;

public class MainPanel extends Composite {

	private static MainPanelUiBinder uiBinder = GWT.create(MainPanelUiBinder.class);

	interface MainPanelUiBinder extends UiBinder<Widget, MainPanel> {
	}

	public MainPanel() {
		
		initWidget(uiBinder.createAndBindUi(this));
		
		Window.alert(Document.get().getElementById("chart1")); //null
		
		
		addAttachHandler(new AttachEvent.Handler() {			
			@Override
			public void onAttachOrDetach(AttachEvent event) {
				Window.alert(Document.get().getElementById("chart1")+""); //not null
			}
		}); 
	}
}


<!DOCTYPE ui:UiBinder SYSTEM "http://dl.google.com/gwt/DTD/xhtml.ent">
<ui:UiBinder xmlns:ui="urn:ui:com.google.gwt.uibinder" xmlns:g="urn:import:com.google.gwt.user.client.ui">
	<g:HTMLPanel>  
	    
	     <div id="chart1"></div>
	   
	</g:HTMLPanel>
</ui:UiBinder>