How to determine whether a tree node is checked or unchecked?

Thanks for your reply.   However it seems not to be able to solve this problem. Here I will describe my problem more clear.



We have some Data Tree and need to check the state of the node. We had hacked the CheckedState of node object in our software in the beginning. Now this hacking is removed from our software. Is  there any other ways to do such checks. 



I also attached a pic to show the checked  and unchecked nodes as an exmaple.



Thanks!