Passing Parameters to Apex Method from Visualforce Page

A question that often crops up when developers are introduced to Visualforce is "how can I pass a parameter to a controller method?".

For example, consider the following page. This outputs the details of up to 10 contacts associated with an account:

<apex:page standardController="Account" extensions="ParamBlogController">
 <apex:outputPanel id="all">
  <apex:form>
    <apex:pageBlock title="Account Detail">
      <apex:pageBlockSection title="Account">
        <apex:outputField value="{!Account.Name}"/>
        <apex:outputField value="{!Account.Description}"/>
      </apex:pageBlockSection>
      <apex:pageBlockSection title="Contacts" columns="1">
        <apex:pageBlockTable value="{!conts}" var="cont" rows="10">
          <apex:column value="{!cont.Id}"/>
          <apex:column value="{!cont.Name}"/>
          <apex:column value="{!cont.Email}"/>
          <apex:column value="{!cont.Phone}"/>
        </apex:pageBlockTable>
      </apex:pageBlockSection>
    </apex:pageBlock>
  </apex:form>
 </apex:outputPanel>
</apex:page>

The controller is as follows - note that I retrieve the contacts and store them in a list rather than relying on the Account.Contacts related list - there is a good reason for this and it will (hopefully) become clear later on:

public class ParamBlogController 
{
 private ApexPages.StandardController stdCtrl {get; set;}
 
 public List<Contact> conts {get; set;}
 
 public ParamBlogController(ApexPages.StandardController std)
 {
  stdCtrl=std;
  setupContacts();
 }
 
 private void setupContacts()
 {
  conts=[select id, Name, Email, Phone from Contact where AccountId=:stdCtrl.getId()];
 }
}

The output of the page is shown below:

Next up I want to add a column that allows various actions to be performed on the particular contact instance.  Its tempting to think that I can just add the following to the markup (assuming I have an appropriate method in the controller) and all will be well:

<apex:column headerValue="Action">
   <apex:commandButton value="Del" action="{!delCont(cont.id)}"/>
</apex:column>

However, this refuses to compile with an error that delCont is an unknown function. As controller action methods can't take parameters in this way, the compiler assumes that this is a formula function, but no function with that name exists, hence the error.

So, how can we pass the id of the contact to the controller? The answer is straightforward, but requires a slight mindshift.

The <apex:param> standard component allows parameters to be defined for a parent component, which can be assigned to a controller property. I can therefore change my markup to the following to specify the parameter:

<apex:commandButton value="Del" action="{!delCont}" rerender="all">
   <apex:param name="contIdParam" value="{!cont.id}" assignTo="{!contIdChosen}"/>
</apex:commandButton>

Note the rerender attribute of the commandbutton - if this attribute is not present, the parameter does not get sent back to the controller. I simply have an outputpanel around the entire page contents.


I then add the following property to my controller:

public String contIdChosen {get; set;}

The key to this is the behaviour when the button is clicked - the id of the contact instance is assigned to my controller property before the action method is invoked. Thus the method that is actually carrying out the delete can simply access the contIdChosen property secure in the knowledge that it will contain the id of the contact associated with the button:

public PageReference delCont()
{
 Contact toDel=new Contact(id=contIdChosen);
 
 delete todel;
 
 setupContacts();
  
 return null;
}

The fact that I have to rerender in order to get the parameter passing to work is the reason why I maintain the list of Contacts independent of the Account record from the standard controller - I can't make the browser refresh the page and thus rebuild the related contacts from scratch, so I have to rebuild the list server side.