param value returns null

Question

I have below VF page.I am passing value from data table.value="{!rlist.Id}" is coming as null.So on button click it is throwing me error for below soql as selectedresourceid =null

CKSW_BASE__Resource__c  res = [select id, name from CKSW_BASE__Resource__c  where id=:selectedresourceid limit 1 ];

Exact error:

System.QueryException: List has no rows for assignment to SObject
Error is in expression '{!rescheduleResource}' in component <apex:commandButton> in page assigntechssp: Class.AssignTechsSPCon.rescheduleResource:

VF page :

<apex:form >
   <apex:actionFunction name="go" action="{!getAllService}" rerender="list">
   </apex:actionFunction>
  <!--  <apex:outputpanel id="key">-->
    <apex:inputtext value="{!searchKey}" onkeyup="go();" id="heroes" html-autocomplete="off"/> 
 <!--    </apex:outputpanel> -->
     <apex:outputPanel id="list" >
        <apex:dataList value="{!serviceList}" var="s" style="width: 164px;overflow-y: hidden;z-index: 1; position : absolute;background-color: #edf2f1;">
          <apex:commandLink value="{!s.Name}"  >
          <apex:param value="{!s.name}" name="serviceId" assignTo="{!serviceId}"/>
          </apex:commandLink>
        </apex:dataList>
     </apex:outputPanel> 

     <apex:dataTable value="{!resourceList}" var="rlist" >
         <!--<apex:column ><apex:selectRadio value="{!rlist.name}">
                        <apex:selectOption value="{!rlist.name}" /> 
                    </apex:selectRadio></apex:column> -->
          <apex:column > <input type="radio" name="nametoselect" value="{!rlist.name}"/>&nbsp;{!rlist.name} &nbsp; {!rlist.Id}
          <apex:param name="selectedresourceid" value="{!rlist.Id}" assignTo="{!selectedresourceid}"/>

          </apex:column> 

         </apex:dataTable>
         <apex:outputText value="{!selectedresourceid}"/><br/>
         <apex:commandButton value="Reschedule resource" action="{!rescheduleResource}" />

</apex:form>

Controller:

public class AssignTechsSPCon {


    public List<CKSW_Base__Service__c> serviceList {get; set;}
    public List<CKSW_BASE__Resource__c> resourceList {get; set;}
    public String searchKey {get; set;}

     public String serviceId{
            get; 
            set
            {
                serviceId= value ;
                searchKey =serviceId;
                System.debug('D : '+serviceId);
            }
        }
         public String selectedresourceid
        {
          get;
          set{
            selectedresourceid=value;
            System.debug('D : '+selectedresourceid);
            }
        }
         public AssignTechsSPCon(){
        resourceList =  new List<CKSW_BASE__Resource__c>()  ; 
        resourceList = [select Id,name from CKSW_BASE__Resource__c ];


        System.debug('resourceList ::'+ resourceList);
        system.debug('selectedresourceid ::'+ selectedresourceid);

    }

    public void getAllService(){

        string soql = 'SELECT Id, Name FROM CKSW_BASE__Service__c WHERE Name like\''+searchKey+'%\'' +' Limit 5';
        System.debug('SOQl ::'+ soql);

        serviceList = Database.query(soql);
        System.debug('serviceList :: '+ serviceList );
        System.debug('serviceId :: '+ serviceId);


       }
     public void rescheduleResource(){
     System.debug('selectedresourceid  :: '+ selectedresourceid );
        CKSW_BASE__Service__c  soqlres = [select id, name, CKSW_BASE__Resource__c from CKSW_BASE__Service__c  where name=:serviceId limit 1 ]; 
        CKSW_BASE__Resource__c  res = [select id, name from CKSW_BASE__Resource__c  where id=:selectedresourceid limit 1 ];
        soqlres.CKSW_BASE__Resource__c = res.name;

        update soqlres;
     }

}

Answer 1

The answer is simple, the tag <apex:param> can only be child of those elements :

<apex:actionFunction>    
<apex:actionSupport>
<apex:commandLink>
<apex:outputLink>
<apex:outputText>
<flow:interview>

you can check it in the official doc:

apex param doc