Salesforce 在apex控制器中维护复选框状态

我正在编写一个visualforce页面，其中用户必须选择我实施分页的机会列表，当用户单击“上一步”按钮时，它将再次呈现列表面板，并且我更改了调用我的visualforce页面段中列表的值

<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>

在自定义控制器中获取OpportunityWrapper列表的代码段为

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;
}

以下是自定义类的公共成员

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

专用整数计数器=0//跟踪偏移量
私有整数列表_size=5；
公共整数总大小；
列出opp；
public List oppwrapper=new List（）//页面中显示的商机包装器列表
公共集合oppId=新集合（）//设置用于维护选中的Id

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我的目标是当我选中任何opportunity包装并转到下一个或上一个列表时，以及当返回时，该项目应处于选中状态，但我得到的设置值始终为空，但我将选择值列表存储在上一个（）方法的集合中，为什么它的显示集始终为空？？？

您可以找到两个解决方案（一个是用JS实现的，另一个是用apex controller实现的）在以下主题中：

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您能找到解决此问题的好方法吗？

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 ;
}

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