property is not set when ring item is clicked - jsf

Question

I have following subpage in Prime faces 3.2:
<ui:composition template="index.xhtml">
<ui:define name="centerContent">
<h:form id="youtubeform">
<h3 style="margin-top: 0">Music</h3>
<p:ring id="basic" value="#{ringView.items}" var="item">
<p:outputPanel style="text-align: center;" layout="block">
#{item.link}
<br />
<p:commandButton update=":youtubeform:itemDetail" icon="ui-icon-search"
title="View" oncomplete="itemDialog.show()" >
<f:setPropertyActionListener value="oka" target="#{ringView.str2}" />
</p:commandButton>
</p:outputPanel>
</p:ring>
<p:dialog header="YoutubeItem Info" widgetVar="itemDialog"
showEffect="fade" hideEffect="fade" resizable="true" width="300" >
<h:outputText id="itemDetail" value="#{ringView.str2}" />
</p:dialog>
</h:form>
</ui:define>
</ui:composition>
and bean:
import java.io.Serializable;
import java.util.ArrayList;
import java.util.List;
import javax.annotation.PostConstruct;
import javax.faces.bean.ManagedBean;
import javax.faces.bean.ViewScoped;
#ManagedBean
#ViewScoped
public class RingView implements Serializable {
private List<YoutubeItem> items;
private YoutubeItem selectedYoutubeItem;
private String str2 = "OK1";
public String getStr2() {
return str2;
}
public void setStr2(String str2) {
this.str2 = str2;
}
public YoutubeItem getSelectedYoutubeItem() {
return selectedYoutubeItem;
}
public void setSelectedYoutubeItem( YoutubeItem selectedYoutubeItem) {
//this.selectedYoutubeItem = new YoutubeItem( "selected" + i);
this.str2 = "setSelectedYoutubeItem";
//this.selectedYoutubeItem = selectedYoutubeItem;
}
#PostConstruct
public void init() {
items = new ArrayList<YoutubeItem>();
items.add( new YoutubeItem( "link1"));
items.add( new YoutubeItem( "link2"));
items.add( new YoutubeItem( "link3"));
//this.selectedYoutubeItem = new YoutubeItem( "selected");
}
public List<YoutubeItem> getItems() {
return items;
}
public void setItems( List<YoutubeItem> items) {
this.items = items;
}
}
The property string str2 is not updated when ring item is called.