common.apex.runtime.impl.ExecutionException: Invalid conversion from runtime type String to List<Id>

Question

While i am clicking addrow button i am getting the below error -

Error -

common.apex.runtime.impl.ExecutionException: Invalid conversion from runtime type String to List<Id>

Kindly let me know where i am doing wrong -

Apex Class -

public with sharing class RFPController{

    public RFP__c accounts;
        public Custom_Package__c del;
        public List < Custom_Package__c > addattendeeList {get;set;}
        public List < Custom_Package__c > delattendeeList {get;set;}
        public List < Custom_Package__c > attendeeList {get;set;}
        public Integer totalCount {get;set;}

        public Integer rowIndex {get;set;}
        public Integer deleterowIndex {get;set;}
        public List < Custom_Package__c > delAttendees {get;set;}
        public Boolean isRerender{get;set;}
         public Integer numberOfRowToRemove { get; set; }
         public String selectedRowIndex{get;set;} 
         public Integer c{get; set;} 
         private List<SelectOption> options;
         public List<SelectOption> AllName{get;set;}
         public List<SelectOption> AllDept{get;set;}

        private List<Custom_Package__c>  acc {get;set;}

        public RFPController(ApexPages.StandardController controller) {

                isRerender = false;
                accounts =  (RFP__c )controller.getRecord();
                String S = 'Select id, Name, Market__c, State__c, First_Issue__c,Last_Issue__c,Circulation__c,Space_Unit__c,Per_Unit_Open_Rate__c,Space_Discount__c from Custom_Package__c ';
                //totalCount = attendeeList.size();
                attendeeList  = Database.Query(S);
                attendeeList = new List < Custom_Package__c >();
                for(integer i=0;i<1;i++){ 
                attendeeList .add(new Custom_Package__c ());
                }
                delattendeeList = new List < Custom_Package__c > ();
                delattendees = new List < Custom_Package__c > ();

                accounts.Rep_Name__c= Userinfo.getuserId();

                AllName = getMarket();
                Alldept = getDept();
        }

        public void addRow() {
                isRerender = true;
               addattendeeList = new List < Custom_Package__c > ();
                attendeeList.add(new Custom_Package__c ());
                //c=c+1;
                //system.debug('@@@@@@add 2' + rowIndex);
        }

    public List<ID> discountScheduleID {
        get {
            if (discountScheduleID == null) {
                discountScheduleID = new List<ID>();
            }
            return discountScheduleID ;
        }
        set;
    }
      public List<SelectOption> getDept()
    {
        List<SelectOption> options = new List<SelectOption>();
        //options.add(new SelectOption('Select','--Select--'));

        for(Custom_Package__c Proj  :[select Id, Name from Custom_Package__c ] )
             {
                    system.debug('3333333'); 
                    options.add(new SelectOption(Proj.ID,Proj.Name));

             }
        return options;

    }
    public List<SelectOption> getMarket(){
        system.debug('^^^^^^^^ Entered' + discountScheduleID );
            List<SelectOption> options = new List<SelectOption>();

         for(Custom_Package__c Proj1  :[select Id,Market__c from Custom_Package__c where ID=:discountScheduleID  ] )
                {
                    system.debug('3333333' + discountScheduleID ); 
                    options.add(new SelectOption(Proj1.ID,Proj1.Market__c ));

                }

        system.debug('^^^^^^^^ Entered' + options.size());        
        return options;


    }
    public List<ID> selectedMarketIds {
        get {
            if (selectedMarketIds == null) {
                selectedMarketIds = new List<ID>();
            }
            return selectedMarketIds ;
        }
        set;
    }
        public void FindAllName()
    {
        AllName= new List<SelectOption>();
        AllDept= new List<SelectOption>();
        system.debug('!!!!!!! Entered');
        AllName = getMarket();
        Alldept = getDept();
        system.debug('&&&&&&& Entered' + AllName );

    }
}

Answer 1

Based on the message, when all the page data is passed back to the controller as a result of the add row button being clicked, a String is being set on a field that has type List<Id>. The two properties of that type are discountScheduleID and selectedMarketIds.

A likely cause is that you have missed the multiselect attribute that causes a list of values to be set:

<apex:selectList value="{!discountScheduleID}" multiselect="true">

Or if only one value should be set don't make the properties list.