Ext.grid.CheckboxSelectionModel复选框设置某行不可以选中

1     var sm = new Ext.grid.CheckboxSelectionModel({    
2        renderer:function(v,c,r){  
3              if(r.get("isEdit")=="可以编辑"){  
4                  return "<div class=\"x-grid3-row-checker\">&#160;</div>";  
5              }else{  
6                  return "";  
7              } 
8          }
9    });