I had a similar challenge, the content of my widget was loading for a few seconds. I display a ""Loading, please wait ..."" label until the widget is loaded:
final VerticalPanel mainPanel = new VerticalPanel();
initWidget(mainPanel);
mainPanel.add(new Label("Loading, please wait ..."));
mainPanel.add(new myCustomWidget()); // this constructor uses RPC to get content
Timer t = new Timer()
{
public void run()
{
if (!mainPanel.getWidget(1).isVisible()) {
// do nothing
} else {
// remove label "Loading, please wait ..."
mainPanel.remove(0);
// stop timer
cancel();
}
}
};
// repeat every 30 miliseconds until myCustomWidget is visible
t.scheduleRepeating(30);