The DataGridView.RowContextMenuStripNeeded event occurs only when the System.Windows.Forms.DataGridView control DataGridView.DataSource property is set or its DataGridView.VirtualMode property is true. Handling the DataGridView.RowContextMenuStripNeeded event is useful when you want to display a shortcut menu determined by a row's current state or the values it contains.
When you handle the DataGridView.RowContextMenuStripNeeded event, the shortcut menu that you specify in the handler is shown whenever the user right-clicks a row unless the DataGridView.CellContextMenuStripNeeded overrides the shortcut menu for the specific cell that was clicked.
The DataGridView.RowContextMenuStripNeeded event also occurs whenever the value of the DataGridViewRow.ContextMenuStrip property is retrieved, either programmatically or when the user right-clicks a row.
You can use the DataGridViewRowContextMenuStripNeededEventArgs.RowIndex property to determine the state of a row or the values it contains, and use this information to change or modify the DataGridViewRowContextMenuStripNeededEventArgs.ContextMenuStrip property. This property is initialized with the value of the row DataGridViewRow.ContextMenuStrip property, which the event value overrides.
Handle the DataGridView.RowContextMenuStripNeeded event when working with large amounts of data to avoid the performance penalties of setting the row DataGridViewRow.ContextMenuStrip value for multiple rows. For more information, see Best Practices for Scaling the Windows Forms DataGridView Control.
For more information about handling events, see Consuming Events.