画虚线需要设置android:layerType="software"，否则无效

一.布局

<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">
<TextView
android:id="@+id/tv_text"
android:gravity="center"
android:layout_centerInParent="true"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:text="下面是虚线"/>
<View
android:layout_below="@id/tv_text"
android:id="@+id/view_line"
android:layout_width="fill_parent"
android:layout_height="2dp"
android:background="@drawable/dotted_line"
android:layerType="software"
/>
</RelativeLayout>

<?xml version="1.0" encoding="utf-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android"
android:shape="line">

<stroke
android:dashGap="20dp"
android:dashWidth="30dp"
android:width="0.5dp"
android:color="@color/abc_input_method_navigation_guard"

/>

</shape>

二.效果图以及描述