Thank you for writing.
In your code, you are trying to change the value of the check box when its cell is clicked. To do that, you need to cast to GridCheckBoxCellElement
sender, Telerik.WinControls.UI.GridViewCellEventArgs e)
((GridCheckBoxCellElement)sender).Value = !(
In order to be able to change the check box by pressing the space key, you need to handle the KeyDown
event of the text box, and do that manually.
Both approaches are implemented in the attached project.
I hope that you find this information useful.
the Telerik team