this.getScreen() is unavailable.

Hi,
I want to load a xml file using RPCManager.loadScreen. But the problem is when I write layout.addChild(this.getScreen()); within execute method, it gives me error.
Can anyone please suggest where i am wrong, Am I missing something.
My source code is.

final Canvas layout = new Canvas();
try{
RPCManager.loadScreen("testXml", new LoadScreenCallback() {

@Override
public void execute() {
layout.addChild(this.getScreen());
}
});
}catch (Exception e) {
e.printStackTrace();
}
//layout.draw();

Tab tab= new Tab();
tab.setPane(layout);
tab.setTitle("XML LOAD");
getEntryprog().tabSet.add(tab);
tab.setCanClose(true);
getEntryprog().programTabSet.addTab(tab);
getEntryprog().programTabSet.selectTab(tab);

My ui.xml is in /webRoot/Shared/ui and code is:

<VLayout xmlns:xsi="http://www.w3.org/1999/XMLSchema-instance" ID="componentsLayout" autoDraw="true">
<members>
<DynamicForm ID="saveForm" autoDraw="false" width="300" titleWidth="100" >
<items>
<item name="cboItem" type="selectitem" defaultValue="Form" width="100"/>
<item name="txtQuantity" type="text" title="Quantity" width="100"/>
<item name="txtItem" type="text" title="Item" />
<item name="txtItem1" type="text" title="Item" />
</items>
</DynamicForm>
</members>
</VLayout>


Please help.

I am using
SmartClient Version: v8.3_2012-11-20/PowerEdition Deployment (built 2012-11-20)

Firefox 25, Chrome 39.0.2171.95 m