How to work with a ComboBox in a DataGridView?

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VB

Gridview

combobox

I'm working with a DataGridView Called "SubDataGridView", where it contains a column of comboboxes. What I intend to do is that when a btn(outside the DataGridView) is pressed, a certain Index is selected in a certain cell,which means the EditingControlShowing Event is excluded .I tried using a DataGridViewComboBoxCell, but the problem is that it does not has the 'SelectedIndex' property. So how can I solve it? More and more I started thinking of getting the children of a certain cell and converting it to a combobox(Note: if this is possible then I need the code responsible for it).