Rules for ids to update components

I'm new to JSF2 and Primefaces and realized an issue to update components.

Lets' assume I have the following piece of code, I can directly update="counter"

<h:form id="f1">
  <h:outputText id="counter" value="#{clientBean.counter}" />
  <h:graphicImage url="/images/circle-ok.png">
    <p:ajax event="click" update="counter" process="@this"
            listener="#{clientBean.tag}"/>
  </h:graphicImage> 
</h:form>

In another h:form I have to use update="f1:counter". Only a update="counter" does not work here.

<h:form id="f2">
  <p:dataT开发者_运维问答able var="var" value="#{clientBean.vf}">
    <p:column> 
      <f:facet name="header">Tag</f:facet>
      <h:graphicImage url="/images/circle-ok.png">
        <p:ajax event="click" update="f1:counter" process="@this"
                listener="#{clientBean.tag}" />
      </h:graphicImage>
    </p:column>
  </p:dataTable>
</h:form>

I haven't faced this with JSF1.2 (and RichFaces), what are the rules to address the ids correctly?

In your first example JSF could lookup up the counter element in the same scope as ajax listener. Form implements NamingContainer which means it prefixes client ids (used in html) with its own id and creates a distinct name space for ids. Have a look at the page source under browser - there will be f1:counter id assigned to your counter. In your second example there is no counter element in the scope (inside form f2) so the lookup fails.

You can disable this form behaviour with prependId="false". This is useful if you are sure there won't be elements with identical ids across all forms.

Icefaces works differently - it automatically calculates the html delta and sends it to the browser as partial update. In most cases this is more convenient for the programmer but comes with considerable performance cost. I believe JSF2 adopted icefaces partial updates concept but requires ids to be passed explicitely.