android ScrollView中嵌套字母索引自定位view，半屏时可以使用Scrollview 滑动展示不全的索引字母

    <?xml version="1.0" encoding="utf-8"?>
    <RelativeLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity"
    android:orientation="vertical"
    android:background="@android:color/background_dark"
    android:gravity="center">
    <Button