<apex:component controller="ComponentController" allowDML="true" id="customcomponent" >
    <apex:attribute name="objectNamecon" description="Value of selcted object" type="String" assignTo="{! objectNameController}" required="true" />
    <apex:attribute name="selectedFieldscon" description="List of selected fields" type="SelectOption[]" assignTo="{! fieldNamesController}" required="true" />
    
    <!-- Tabstyle attribute is used to assign the color scheme to the pageblock.Here Account Object color scheme is used for the pageblock-->
    <apex:pageBlock id="pgblock" title="{!objectNameController} details" >
        <table style="width: 100%">
            <tr>
                <td>
                    <apex:commandButton value="New Record" action="{! newRecord }" />&nbsp;
                    <apex:commandButton value="Delete Selected" action="{! deleteSelectedRecords}" reRender="pgblock" />&nbsp;
                    <apex:commandButton value="Download CSV" action="{! newRecordCSV}" />
                </td>                
            </tr>
        </table>
        <apex:pageBlockSection columns="1" collapsible="false" id="pgBlockSection">
            <apex:pageBlockTable value="{!retrieveRecords }" var="row">
               
                <b><apex:column id="checkboxcolumn" >
                    <apex:facet name="header">
                        <apex:inputCheckbox id="headerCheckbox" value="{! checked}" >
                            <apex:actionSupport event="onchange" action="{! headerCheckboxMethod}" reRender="pgblock"/>
                        </apex:inputCheckbox>
                    </apex:facet>
                    <apex:inputCheckbox value="{!row.isChecked}" id="childCheckBox" >
                        <apex:actionSupport event="onchange" action="{! checkboxStateMethod}" reRender="headerCheckbox, childCheckBox">
                            <apex:param name="checkboxId" value="{! row.Sobj.Id}" assignTo="{! recordId}" />
                        </apex:actionSupport>
                    </apex:inputCheckbox> 
                </apex:column></b>
                
                <apex:column headerValue="Action" title="Action">
                    <apex:outputLink title="Edit Record" value="/{! row.Sobj.Id}/e?retURL=/apex/DescribeCallAssignment" >Edit</apex:outputLink>|&nbsp;
                    <apex:commandLink title="Delete Record" action="{! deleteRecord}"  reRender="pgblock">Del
                        <apex:param name="recordToBeDeleted"  value="{! row.Sobj.Id}" assignTo="{! RecordToDelete}" />
                    </apex:commandLink>
                </apex:column>
                <apex:repeat value="{! retrieveColumns}" var="col">
                    <apex:column value="{! row.Sobj[col]}" />
                </apex:repeat>
            </apex:pageBlockTable>
        </apex:pageBlockSection>
        
        <table style="width: 100%">
            <tr>
                <td>               
                    <apex:selectList value="{! recordPerPage }" size="1">
                        <apex:selectOption itemLabel="5" itemValue="5" />
                        <apex:selectOption itemLabel="10" itemValue="10" />
                        <apex:selectOption itemLabel="15" itemValue="15" />
                        <apex:selectOption itemLabel="20" itemValue="20" />
                        <apex:actionSupport event="onchange" reRender="pgblock" />
                    </apex:selectList>
                </td>
                <td align="center">
                    <apex:commandButton value="First" action="{! FirstPage }" disabled="{! HasPreviousPage}" reRender="pgblock" />
                    <apex:commandButton value="Previous" action="{! PreviousPage }" disabled="{! HasPreviousPage}" reRender="pgblock" />
                    <apex:commandButton value="Next" action="{! NextPage }" disabled="{!HasPNextPage}" reRender="pgblock" />
                    <apex:commandButton value="Last" action="{! LastPage }" disabled="{!HasPNextPage}" reRender="pgblock" />
                </td>
                <td align="right">
                    <apex:outputText value="Page {! IF(( offset ==0 ), 1, (numberOfRecords / recordPerPage)) } of {! CEILING(numberOfRecords / recordPerPage) }"></apex:outputText>
                </td>
            </tr>
        </table>        

    </apex:pageBlock>        
</apex:component>

public class ComponentController {
    
    //Required Variables-----------------------------------------
    public String objectNameController{ get; set; }
    public List<SelectOption> fieldNamesController{ get; set; }    
    public Integer offset{ get; set; }
    public Integer recordPerPage{ get; set; }
    public Integer numberOfRecords{ get; set; }
    public String characterForSort{ get; set; }
    public Id RecordToDelete{ get; set; }    
    public Id recordId{ get; set; }
    public Boolean checked{ get; set; }
    public Boolean checkChild{ get; set; }
    
    
    //Private Variables-----------------------------------------
    private String query;
    private List<String> columnList;
    private String recordsToPass;
    public Map<Id, Boolean> checkboxState{ get; set; }
    public String passQuery{ get; set; }
    
    //Constructor-----------------------------------------
    public ComponentController(){ 
        offset = 0;
        recordPerPage = 5;
        characterForSort = '';
        numberOfRecords = [SELECT COUNT() FROM Account];
        checkboxState = new Map<Id, Boolean>();
        passQuery = '*';
        checked = false;
        checkChild = false;
    }
    
    //Method for query generation-----------------------------------------
    private String QueryGenerator(){
        
        String str;
        for(Integer i=0; i<fieldNamesController.size(); i++){
            if( i == 0 )
                str = ( 'SELECT ' + fieldNamesController.get(i).getValue() );
            else
                str += ( ', ' + fieldNamesController.get(i).getValue() );
        }
        str += ' FROM ' + objectNameController;
        return str;
    }
    
    //Method for column generation-----------------------------------------
    private List<String> columnListGenerator(){
        List<String> colList = new List<String>();
        for(SelectOption soption : fieldNamescontroller){
            colList.add(soption.getValue());
        }
        return colList;
    }
    
    //Method for getting records to dispay in the table-----------------------------------------
    public List<SobjectWrapper> getretrieveRecords(){
        query = QueryGenerator();
        recordsToPass = query;
        query += (' LIMIT ' + recordPerPage + ' OFFSET ' + offset);
        //return Database.query(query);
        list<SobjectWrapper> lstSobjectWrapper = new list<SobjectWrapper>();
        for(Sobject Obj : Database.query(query)){
            SobjectWrapper wrapperObj = new SobjectWrapper();
            wrapperObj.sobj = Obj;
            wrapperObj.isChecked = (passQuery != null && passQuery.contains(Obj.Id)) ? true : false;
            lstSobjectWrapper.add(wrapperObj);
        }
        return lstSobjectWrapper;
    }
    
    
    //Method for getting columns to display in the table-----------------------------------------
    public List<String> getretrieveColumns() {
        columnList = columnListGenerator();
        return columnList;
    }
    
    //Method on New Record Button-----------------------------------------
    public PageReference newRecord(){
        sObject testRec = Database.query('Select Id from '+ objectNameController +' Limit 1');
        String keyPrefix = String.valueOf(testRec.Id).subString(0, 3);
        PageReference page = new  PageReference('/'+keyPrefix+'/e');
        page.setRedirect(true);
        return page;
    }
    
    //Method on Delete Selected Button
    public void deleteSelectedRecords(){
        List<sObject> recList = new List<sObject>();
        Set<Id> idSet = checkboxState.keySet();
        for(sObject obj : Database.query('SELECT Id FROM '+objectNameController+' WHERE Id in :idSet')){
            recList.add(obj);
        }
        checked = false;
        delete recList;
    }
    
    //Method which directs to CSV download page-----------------------------------------
    public PageReference newRecordCSV(){
        PageReference page;
        if( checkboxState.size() == 0 ){            
            page = new  PageReference('/apex/csvDownloadPage?records='+recordsToPass);
        }
        else{
            passQuery += ('**'+objectNameController+'***');
            for(Integer i=0; i<fieldNamesController.size(); i++){
                if( i == 0 )
                    passQuery += ( fieldNamesController.get(i).getValue() );
                else
                    passQuery += ( ', ' + fieldNamesController.get(i).getValue() );
            }
            passQuery += '****';
            System.debug(passQuery);
            page = new  PageReference('/apex/csvDownloadPage?records='+passQuery);
        }
        
        page.setRedirect(true);
        return page;
    }
    
    //Method on header Checkbox-----------------------------------------
    public void headerCheckboxMethod(){
        List<sObject> objList = Database.query('SELECT Id FROM '+ objectNameController);
        if( checkboxState.size() != objList.size() ){
            checkboxState.clear();
            passQuery = '*';
            for(sObject temp : objList){
                checkboxState.put(temp.iD, true);
                passQuery += (String.valueOf(temp.Id)+',');
            }
        }
        else{
            checkboxState.clear();
            passQuery = '*';
        }
        
        if(!checked){ 
            checked = true;
            checkChild =true;
            System.debug(checked+' ===== '+checkChild);
        }
        else{
            checked = false;
            checkChild = false;
        }
    }
    
    //Method to maintain Checkbox State-----------------------------------------
    public void checkboxStateMethod(){
        List<sObject> objList = Database.query('SELECT Id FROM '+ objectNameController);
        System.debug('Record Id ==== ' + recordId);
        if( checkboxState.containsKey(recordId) ){
            checkboxState.remove(recordId);
            passQuery = passQuery.remove(String.valueOf(recordId)+',');
            System.debug('Map ==== ' + checkboxState);
            System.debug('Query String ==== ' + passQuery);
        }
        else{
            checkboxState.put(recordId, true);
            passQuery += (String.valueOf(recordId)+',');
            System.debug('Map ==== ' + checkboxState);
            System.debug('Query String ==== ' + passQuery);
        }

        if(checkboxState.size() == objList.size()){
            checked = true;
        }
        else{
           checked = false;
        }   
    }
    
    
    //Method on Delete Action-----------------------------------------
    public void deleteRecord(){
        sObject obj = Database.query('SELECT Id FROM '+objectNameController+' WHERE Id = \''+RecordToDelete+'\'');
        try {            
            delete obj;
        } catch (DmlException e) {}
    }
    
    public class SobjectWrapper{
        public boolean isChecked{get;set;}
        public Sobject Sobj{get;set;}
        public SobjectWrapper(){
            isChecked = false;
            
        }
    }    

    
    
    //Pagination methods-----------------------------------------
    public void Firstpage(){ offset = 0; }    
    public void Previouspage(){ offset -= recordPerPage; }
    public void Nextpage(){ offset += recordPerPage; }
    public void Lastpage(){ offset = (((numberOfRecords)/recordPerPage)*recordPerPage); }
    
    //Boolean pagination methods-----------------------------------------
    public Boolean HasPreviousPage{ 
        get{ 
            if(offset == 0 ){
                return true;
            }
            return false;
          }
    
        set;
    }
    
    public Boolean HasPNextPage{ 
        get{ 
            if(offset == (((numberOfRecords)/recordPerPage)*recordPerPage) ){
                return true;
            }
            return false;
          }
        set;
    }  
    
}