<?xml version="1.0" encoding="utf-8"?>
<paths xmlns:android="http://schemas.android.com/apk/res/android">
    <!--因为要安装的apk是存储在sd卡的，这里的映射就相当于:
     content:虚拟路径 映射到了-> Environment.getExternalStorageDirectory()
    -->
    <external-path
        name="external_path"
        path="." />
</paths>