can not select the combox value

var itemTextArray = ["Home", "Favorites", "Font size", "Search"];
var itemImageArray = ["home", "favorites", "fontsize", "search"];
var combo = new AW.UI.Combo;
combo.setId("combo1");
combo.setControlText("Combo");
combo.setControlImage("favorites");
combo.setItemText(itemTextArray);
combo.setItemImage(itemImageArray);
combo.setItemCount(4);
var grid2 = new AW.Grid.Extended;
grid2.setId("grid2");
grid2.setCellText("cell");
grid2.setHeaderText("header");
grid2.setFooterText("footer");
grid2.setFooterVisible(true);
grid2.setColumnCount(5);
grid2.setRowCount(10);

grid2.setCellTemplate(combo, 1,1);

grid2.refresh();
<r> can not select the combox value</r>