Change icon of a grid row

[hieu79vn]

Hi
I would like to do like the first column in this example
http://dev.sencha.com/deploy/ext-4.1.0-gpl/examples/simple-tasks/index.html
W (http://dev.sencha.com/deploy/ext-4.1.0-gpl/examples/simple-tasks/index.html)hen we click on a red check, it will change to a gray check. Could you show me where is the code to do that. I have read the one of this example but cannot understand

Thanks

[Tim Toady]

They used a check column
http://docs.sencha.com/ext-js/4-1/#!/api/Ext.ux.CheckColumn