to fill xml data into grid

hi,

I have xml data in my string and I try to fill this data in a grid but I cannot have it done. In a button click event I am doing the following:
button.onClick = function()
{
table.setXML(xml);  
Grid.setHeaderCount(1);
Grid.setColumnCount(4);
Grid.setRowCount(3);
Grid.setColumns(columnNodes);                   
Grid.setCellEditable(true);                
Grid.setCellModel(table);  
Grid.refresh();
}