The CellValidating event handler is where you determine whether the value of a cell in the SchoolName column is empty. If the cell value fails validation, set the Cancel property of the System.Windows.Forms.DataGr... class to true. This causes the DataGridView control to prevent the cursor from leaving the cell. Set the ErrorText property on the row to an explanatory string. This displays an error icon with a ToolTip that contains the error text. In the CellEndEdit event ......