TextChanged event are not working for DataGridViewComboBoxCell with DropDown Style in c#

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C#

here is my code

private void dataGridView1_EditingControlShowing(object sender, DataGridViewEditingControlShowingEventArgs e)
  {
    if (e.Control.GetType() == typeof(DataGridViewComboBoxEditingControl))
    {
      DataGridViewComboBoxEditingControl combo = e.Control as DataGridViewComboBoxEditingControl;
      combo.DropDownStyle = ComboBoxStyle.DropDown;
      combo.TextChanged += new EventHandler(combo_TextChanged);
    }
  }

i want to change my DataGridViewComboBoxCell style to dropdown..(to change the combobox DropDownStyle to allow for the user to enter text while the combobox is in edit mode)
but unfortunately, the standard DataGridView does not allow this to happen at Design-Time so i want to pull some tricks. When the field loses focus and the edit control is no longer available, the combobox reverts its style. Therefore, the validating event is being used to add values into the list of available values so that the items can still be displayed correctly.

pls help me,

-tushar