Getting Checked rows from gridview in asp.net

I have a GridView in ASP.net where I have a CheckBox column. The user can toggle the CheckBox. Now, what I want is that when the user clicks on a button, all the records from the GridView where the CheckBox is checked should be displayed. And on another button, the opposite state should be displayed…
I am not getting the logic for the same.

Keeping radio/checkbox values on postback?

There’s is something I don’t get with ASP objects. I have a button in a update panel. On the same page, I have a checkbox, a radiobutton and a textbox (outside the update panel). When I click on my button, I access all those three objects. The textbox is able to keep the his text value. But the radio/checkbox always return false when I check there checked state.