更改自定义AutoCompleteTextView的下划线颜色

<style name="CustomAutoCompleteTextView" parent="Widget.AppCompat.AutoCompleteTextView">
    <item name="android:background">@drawable/custom_edittext_background</item>
</style>

<shape xmlns:android="http://schemas.android.com/apk/res/android">
    <solid android:color="#00000000" /> <!-- 设置背景颜色为透明 -->
    <stroke
        android:width="2dp"
        android:color="#FF0000" /> <!-- 设置下划线颜色为红色 -->
</shape>

<AutoCompleteTextView
    android:id="@+id/autoCompleteTextView"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    style="@style/CustomAutoCompleteTextView" />