<?xml version="1.0" encoding="utf-8"?>
<!--空心圆角矩形  -->
<shape xmlns:android="http://schemas.android.com/apk/res/android"
    android:shape="rectangle" >
    <corners android:radius="10dp" /><!-- 圆角半径 -->
    <gradient
        android:endColor="@color/colorPrimary"
        android:startColor="@color/colorAccent" /><!-- 矩形的内部颜色，这里设置成白色，即空心 -->
</shape>