I have a checkbox selection model on a grid panel. The configuration of the CheckboxModel like this:

`selMode:{
selType:'checkboxmodel'
checkOnly: true,
headerText:"Select All",

listeners:{

'select':function(this, record, index){

if(this.selected.items.length == this.store.data.length){

// I want to update **headerText** here 
//when all the records's checkboxes are checked 

}
}
}
}`

Initially, headerText is “Select All” which is fine but when the user selects All records it should be “Unselect All”.I want to update headerText dynamically.