AutoCompleteTextView Web Requests + Dropdown is gone

I'm implementing a AutoCompleteTextView which takes the content from a RESTAPI. This is working, but the dropdown list is never shown, so the user can't select a item. In开发者_如何学C "afterTextChanged" I call an AsyncTask and the data will be downloaded. That's working. If I use showDropDown() nothing will happen. How can I force that the DropDownList is shown evry time?

Thanks for your help !