using CheckboxSelectionModel to select multiple rows

Code:

var  xg = Ext.grid;

var  checkboxSelector = new  xg.CheckboxSelectionModel({
    header:'',
handleMouseDown:Ext.emptyFn,
listeners : {
        'rowselect': function (selectionModel, rowIndex, record){
            var  valueSelected = record.get ('actionId');
}
    }
});


var  erroneousActionsGrid = new  xg.GridPanel({
    id:'erroneousActionsPanel',
layout: 'fit',
store: store,
cm: new  xg.ColumnModel([
        checkboxSelector,
{header: "Action Name", width: 80, sortable: true , dataIndex: 'actionName'},
{header: "Action Id", width: 30, sortable: true , dataIndex: 'actionId'},
{id:'files',header: "File Id", width: 30, sortable: true , dataIndex: 'fileId', renderer: function (value, metaData, record, rowIndex, colIndex, store) {return  '<a href=file/lifeCycleFile/'+ value +'>' + value +'</a>'; }},
{header: "Task Id", width: 30, sortable: true , dataIndex: 'taskId'},
{header: "User Name", width: 50, sortable: true , dataIndex: 'userName'},
{header: "Execute Date", width: 30, sortable: true , dataIndex: 'executeDate', renderer: Ext.util.Format.dateRenderer('Y/m/d H:i:s')}
    ]),
bbar: actionListPagingBar,
plugins: [{
        ptype: 'perpagefield',
beforeText: ''
}],
sm: checkboxSelector,

using CheckboxSelectionModel to select multiple rows