How do I set cell to blank in a Combo box column at a datagridview

I have a DataGridView that contains one ComboBox column. the datagridview gets data from a table. the combo box has datasource from another table that contains two columns, one is ID and the another is name. I set the ID field as the combobox valuemember and set the name field as the conbo box dispalymember. everything works fine. the problem is that if a cell originally is blank. I select a value from combo box for the sell, then I find I made amistake and want to undo it. it cannot change the cell back to blank. Anyway can we do this. please help. Thanks.
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Hi JackXiang :

That’s a default behavior of Drop Down Box implemented by .Net.

If you really want to solve this, you have to add one more additional value in your Data Source something like Display Member “SELECT” and Value = 0/-1.

On a different note I have a query, What exactly undo means. Either you want to change the value from dropdown or don’t want to select anything. #1 you can do and for #2 directly delete the Row.

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