ComboBox Exposure

I have a ComboBox. When that ComboBox get the focus, I’d like to have it show all the available choices rather that the one selected. The effect would be the same as when the user clicks on the down arrow in the ComboBox.

Is this doable?

i not see any method that open this list.
maybe replace this combo box as textfield + list button (container control) and open a list in a extra window and after select u raise a event in the window where the control is placed, so you can read the new value and close the pop up there.