renderInfo.get not get initiated

I have this code in my application to get properties for the “middelContainer” component. How is the call to " infoReceived(RenderInfo info) is initiated? It seems this method is never being called? I am on the server side. can you help how to initiate this call to get property value?? Thank you

RenderInfo.get(middleContainer, new Callback() {
public void infoReceived(RenderInfo info) {
for (CssProperty prop : CssProperty.values()) {