How to prevent a control to loose focus when clicking a button

You can't prevent a control from losing focus while granting another control focus. (You can prevent focus loss on editing controls by using the Validating event and its Cancel EventArgs, but this prevents the button from receiving focus and clicking.) Likely what you'll need to consider doing is keep a reference variable for the currently selected datagrid cell that you update as different cells are selected, then when you click an applicable button, use the referenced cell object to update its text or perform whatever actions you were considering with SendKeys.