How to get Active object

[Deepak]

Hi,

I am developing an Add-in. The requirement are:

1. User will select a table or chart object in the slide.
2. then he will invoke the add in which display a simple text box.
3. user can give a unique name to the selected table or chart. this name
should be unique in the file.

Please suggest how this can be achieved? i am just starting the development
but unable to get the Active object?

Thanks
Deepak