build.gradle  manifestPlaceholders 设置

 manifestPlaceholders = [
                XG_ACCESS_ID: "2100209996",
                XG_ACCESS_KEY: "AHW931HVZ42A",
                HW_APPID: "100225811",
                PACKAGE_NAME: "com.jeepeng.push"
        ]

这里的配置起到的作用是什么？？ 代码中配置的优先级是哪个