This recipe makes use of a custom controller, so this will need to be created before the Visualforce page.

Opening the following URL in your browser shows the list of currently open opportunities: https://<instance>/apex/ActionParameter.

Here, <instance> is the Salesforce instance specific to your organization, for example, na6.salesforce.com.

Clicking on the Win button for the Grand Hotels Kitchen Generator opportunity updates the status to Closed Won and redraws the list of opportunities.

The page markup to send the parameter to the controller is as follows:

<apex:commandButton value="Win" action="{!winOpp}" status="status"
        rerender="opps_pb" 
        rendered="{!opp.StageName!='Closed Won'}">
   <apex:param name="oppIdToWin" value="{!opp.Id}" 
assignTo="{!oppIdToWin}" />
</apex:commandButton>

The <apex:param /> component defines the value of the parameter, in this case, the ID of the opportunity, and the controller property that the parameter will be assigned to – oppIdToWin.

The property is declared in the controller in a normal way.

public Id oppIdToWin {get; set;}

Finally, the action method is invoked when the button is pressed.

public PageReference winOpp()
{
   Opportunity opp=new Opportunity(Id=oppIdToWin,
                                   StageName='Closed Won');
   update opp;
   return null;
}

The ID of the opportunity to update is assigned to the oppIdToWin controller property before the action method is invoked; thus, the action method can simply access the property to get the parameter value.