Keyboard covers the last item of an AutoCompleteTe

问题:

I am developing an app for Android, which is supposed to behave like a lightweight modal box that presents a drop-down to search and choose stuff from. I decided to use the AutoCompleteTexView for that. My question is, why does the keyboard happen to cover part of the items? I though that AutoCompleteTextView will automatically move up to give space to the keyboard. It doesn't. In fact, it hangs at about the middle of the screen.

The layout that is holding the ACTV is a simple LinearLayout with vertical orientation.