apex:actionRegion

1<!-- For this example to render fully, associate the page
2with a valid opportunity record in the URL.
3For example: https://Salesforce_instance/apex/myPage?id=001D000000IRt53 -->
4
5<apex:page standardController="Opportunity">
6  <apex:form >
7    <apex:pageBlock title="Edit Opportunity" id="thePageBlock" mode="edit">
8
9      <apex:pageBlockButtons >
10        <apex:commandButton value="Save" action="{!save}"/>
11        <apex:commandButton value="Cancel" action="{!cancel}"/>
12      </apex:pageBlockButtons>
13
14    <apex:pageBlockSection columns="1">
15      <apex:inputField value="{!opportunity.name}"/>
16      <apex:pageBlockSectionItem>
17      <apex:outputLabel value="{!$ObjectType.opportunity.fields.stageName.label}"
18                        for="stage"/>
19      <!--
20           Without the actionregion, selecting a stage from the picklist would cause
21           a validation error if you hadn't already entered data in the required name
22           and close date fields.  It would also update the timestamp.
23      -->
24      <apex:actionRegion>
25        <apex:inputField value="{!opportunity.stageName}" id="stage">
26          <apex:actionSupport event="onchange" rerender="thePageBlock"
27                              status="status"/>
28          </apex:inputField>
29          </apex:actionRegion>
30      </apex:pageBlockSectionItem>
31        <apex:inputfield value="{!opportunity.closedate}"/>
32        {!text(now())}
33        </apex:pageBlockSection>
34
35      </apex:pageBlock>
36    </apex:form>
37</apex:page>