Ext.grid.CheckboxSelectionModel 控制某行没有checkbox

var detailSM = new Ext.grid.CheckboxSelectionModel({
renderer:function(value,metaData,record){
if(record.get("shbz") == "CHECKSTATE_YES" ){
return;
}else{
return Ext.grid.CheckboxSelectionModel.prototype.renderer.apply(this,arguments);  
}
},
listeners:{
"beforerowselect" : function(selectionModel,rowIndex,keepExisting,record){
if(record.get("shbz") == "CHECKSTATE_YES"){
//Ext.Msg.alert("提示","该行数据不能能做删除操作");
return false;
}else{
return true;
}
}
}
});