Maintaining CheckBox status in apex controller

Question

i am writing a visualforce page in which user has to select list of Opportunity i implemented pagination when user click previous button then it will render list panel again and i changed the value of list in the call my visualforce page segment is

<apex:pageBlockTable value="{!numbers}" var="n" align="center">
    <apex:column >
        <apex:inputCheckbox value="{!n.checked}"/>
    </apex:column> 
    <apex:column value="{!n.cat.Id}" />
    <apex:column value="{!n.cat.Name}" />
    <apex:facet name="footer">Showing Page # {!pageNumber} of {!totalPages}</apex:facet>
</apex:pageBlockTable>

I have an OpportunityWrapper class for maintaining checkItem:

public class OpportunityWrapper {
    public Boolean checked { get; set; }
    public Opportunity cat { get; set; }

    public OpportunityWrapper(){
        cat = new Opportunity();
        checked = false;
    }

    public OpportunityWrapper(Opportunity c){
        cat = c;
        checked = false;
    }

    public OpportunityWrapper(Opportunity c, Boolean checked){
        cat = c;
        this.checked = checked ;
    }
}

The segment of code for getting list of OpportunityWrapper in custom controller is

public List<OpportunityWrapper> getNumbers() {
    opp = new List<OpportunityWrapper>();
    if ( selectedPage != '0' )
        counter = list_size*integer.valueOf(selectedPage)-list_size;

    //we have to catch query exceptions in case the list is greater than 2000 rows
    try {
        for ( Opportunity o : [SELECT Id,Name from Opportunity order by name 
               limit :list_size offset :counter] ) {
            if ( !oppId.contains(o.Id) ) 
                opp.add(new OpportunityWrapper(o));
            else
                opp.add(new OpportunityWrapper(o,true));               
        } 
    } catch ( QueryException e ) {
        ApexPages.addMessages(e);                   
        return null;
    }    
    return opp;
}

and when the previous button is pressed following method is called

public PageReference Previous() {
    //user clicked previous button
    for ( OpportunityWrapper o : opp ) { 
        if ( o.checked &&  oppId.contains(o.cat.Id) )
            oppId.add(o.cat.Id); 
    }
    selectedPage = '0';
    counter -= list_size;
    return null ;
}

and the following are public member of custom class

private integer counter = 0;  //keeps track of the offset
private integer list_size = 5;
public integer total_size; 
List<OpportunityWrapper> opp ;
public List<OpportunityWrapper> oppwrapper = new List<OpportunityWrapper>(); //list of Opportunity wrapper shown in the page
public  Set<String> oppId = new Set<String>(); //set for maintaining which Id's are checked

My target is when I checked any opportunity wrapper and goto next or previous list and when return back that item should be in checked but i am getting set value always empty but i am storing list of select value in the set of Previous() method why its showing Set always empty??

Pavel Slepiankou Pavel Slepiankou · Accepted Answer · 2013-02-23T18:14:09

you can find out 2 solutions (one implemented with JS and another one with apex controller) in the following topic:

How to find out which checkboxes have been selected on the next page in VisualForce?

Maintaining CheckBox status in apex controller

1 Answers