how to make SelectorWidth dinamic?

i have this one but first time grid load dont work, i make reset grid and this work fine, some one know how can i make this dinamic?

obj.onTotalRowChanged = function(value) {
var sTlen = this.getTotalRowCount().toString().length;
if ( sTlen>2 ){
this.setSelectorWidth(parseInt(sTlen*8));
}else{
this.setSelectorWidth(20);
}
};