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"
    ……