如何在GWT中设置属性?

DOM.setElementAttribute ,我做错什么了吗?

class MyListBox extends com.google.gwt.user.client.ui.ListBox {
  ....
  protected void setHoverAutoWidth() {
    addDomHandler(new MouseOverHandler() {
      public void onMouseOver(MouseOverEvent event) {
        DOM.setElementAttribute(getElement(), "width", "auto");
      }
    }, MouseOverEvent.getType());
    addDomHandler(new BlurHandler(){
      public void onBlur(BlurEvent event) {
        DOM.setElementAttribute(getElement(), "width", "100px");
      }
    }, BlurEvent.getType());
  }
}

(我知道改变宽度的方法比直接设置style属性要少,但我现在不关心css。)

编辑: