How to activate combobox on first click (Datagridview)

Set the following on your DataGridView:

EditMode = EditOnEnter

This is probably the easiest solution and has been the workaround for many users here on SO when this question gets asked.

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EDIT :

Per here do the following:

Set the Editmode:

EditMode = EditOnKeystrokeOrF2

Modify the EditingControlShowing event on the datagridview:

private void dataGridView1_EditingControlShowing(object sender, DataGridViewEditingControlShowingEventArgs e)
{
    ComboBox ctl = e.Control as ComboBox;
    ctl.Enter -= new EventHandler(ctl_Enter);
    ctl.Enter += new EventHandler(ctl_Enter);

}

void ctl_Enter(object sender, EventArgs e)
{
    (sender as ComboBox).DroppedDown = true;
}

This will get you your desired results. Let me know if that doesn't do it.

I realize this is an old question, but I figured I would give my solution to anyone out there that may need to be able to do this.

While I couldn't find any answers to do exactly this... I did find an answer to a different question that helped me.

This is my solution:

private void datagridview_CellEnter(object sender, DataGridViewCellEventArgs e)
    {
        bool validClick = (e.RowIndex != -1 && e.ColumnIndex != -1); //Make sure the clicked row/column is valid.
        var datagridview = sender as DataGridView;

        // Check to make sure the cell clicked is the cell containing the combobox 
        if(datagridview.Columns[e.ColumnIndex] is DataGridViewComboBoxColumn && validClick)
        {
            datagridview.BeginEdit(true);
            ((ComboBox)datagridview.EditingControl).DroppedDown = true;
        }
    }


private void datagridview_CurrentCellDirtyStateChanged(object sender, EventArgs e)
    {
        datagridview.CommitEdit(DataGridViewDataErrorContexts.Commit);
    }

The above code must be tied into the CellEnter event of the datagridview.

I hope this helps!

edit: Added a column index check to prevent crashing when the entire row is selected.

Thanks, Up All Night for the above edit

edit2: Code is now to be tied to the CellEnter rather than the CellClick event.

Thanks, HaraldDutch for the above edit

edit3: Any changes will committed immediately, this will save you from clicking in another cell in order to update the current combobox cell.