TextInputLayout and AutoCompleteTextView

Now, with AndroidX you don’t need customise something.
Need just add material component style (was added in 1.1.0-alpha06, see release notes).

<com.google.android.material.textfield.TextInputLayout
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:hint="Example TextInputLayout">

    <androidx.appcompat.widget.AppCompatAutoCompleteTextView
    style="@style/Widget.MaterialComponents.AutoCompleteTextView.FilledBox"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"/>

</com.google.android.material.textfield.TextInputLayout>