In VB6 you could set the initial value held in ComboBox control to -1 so that it is blank to begin with. But in .NET if when the DataSource property is set for a ComboBox, you cannot modify the item collection. You cannot set ComboBox1.Text = "" or use Add method to add a new item to the list.
So how would you add a blank value to the ComboBox item collection, when it is bound to a data source?
The DataSource property of ComboBox accepts an object that implements the IList interface, such as a DataSet. Although you cannot modify the item collection, you can actually add a blank data row in DataSet which is bound to ComboBox. The new blank row will be shown in the ComboBox.