Popupmenu doesn't show up when listening to onClick

<zk>
<menubar>
	<menu label="Menu1" onClick="//do something">
		<menupopup>
			<menu label="New">
				<menupopup>
					<menuitem label="Small Car" />
					<menuitem label="Mediem Car" />
					<menuitem label="Large Car" />
				</menupopup>
			</menu>
			<menuitem label="Search" />
		</menupopup>
	</menu>
	<menu label="Menu2">
		<menupopup>
			<menu label="New">
				<menupopup>
					<menuitem label="Small Car" />
					<menuitem label="Mediem Car" />
					<menuitem label="Large Car" />
				</menupopup>
			</menu>
			<menuitem label="Search" />
		</menupopup>
	</menu>
</menubar>
<label multiline="true">
	1.in ipad 
	2.click on menu1 or menu2, it should show menupopup
</label>
</zk>