今天在调试Android网络模块（用的Retrofit+OKHttp）的时候报错：
java.net.UnknownServiceException: CLEARTEXT communication ** not permitted by network security policy
解决方案：
首先在 rsc/xml 目錄下建立 network_security_config.xml
<?xml version="1.0" encoding="utf-8"?>
<network-security-config>
<base-config cleartextTrafficPermitted="true" />
</network-security-config>
然后在Manifest.xml中添加属性：
<application
android:networkSecurityConfig="@xml/network_security_config"
……
