DataGrid – Edit the selected row when a button is clicked-Collection of common programming errors

I have a very simple DataGrid with 2 columns, some thing like this:

What Im trying to do is to activate the edition of the selected row when the user clicks a button. So far I’ve been unable to find any example of how to do this. I already tried 6 or 7 different approaches but non works. Does any one has a clue how to do this?

How do you get the selected row (NOT selectedItem) of a DataGrid and how can you:

• Change the ItemRenderEditor or ItemRenderer on the fly of just that row.
• Or enable the edition of that specific row without clicking it.

This are the questions that I’ve been unable to answer

Help will be greatly appreciated.