Example showing how to read a build number from a CI system for automatic build numbers

app_build.gradle

android {

    //version.properties is only used to get the version number from CircleCi
    def versionFile = file('../.signing/version.properties')
    def buildNumber = 456

    if(versionFile.canRead()) {
        Properties props = new Properties()
        props.load(new FileInputStream(versionFile))

        //Add skip_appcenter_release in a commit message to develop/master/release if you don't want a build to be created by CircleCi
        if(props['VERSION_CODE'] != null) {
            def circleBuildNumber = props['VERSION_CODE'].toInteger()
            buildNumber = circleBuildNumber - 3870 //subtract offset to get close to our real build number
        }
    }

    defaultConfig {
        versionCode buildNumber
        versionName "1.2.3"
    ...

    }

...

}