Remove underline from AutoCompleteTextView via xml

This will also work properly

android:inputType="textNoSuggestions"

android:inputType="textPhonetic"

Just put:

android:background="@android:color/transparent"

inside your view.

EDIT: As @kiya said, nowadays is better to use

android:backgroundTint="@android:color/transparent"

As it maintains the view size.