app_build.gradle

/**
 * Auto increment versionCode for every build
 * read version.properties in android root directory and auto increment build number on release
 */
def readAndIncrementVersionCode() {
  def isRelease = false
  List<String> runTasks = gradle.startParameter.getTaskNames();

  for (String item : runTasks) {
    if (item.contains("assemble") && item.contains("Release")) {
      isRelease = true;
    }
  }

  def versionFile = new File(project.rootDir, 'version.properties')

  // read
  def version = new Properties()
  def stream
  try {
    stream = new FileInputStream(versionFile)
    version.load(stream)
  } catch (FileNotFoundException ignore) {
    println "version.properties not found"
  } finally {
    if (stream != null) stream.close()
  }
  def versionCode = version['versionCode'] ? version['versionCode'] as int : 0

  // increment by 1 in release
  if (isRelease) {
    versionCode += 1
    version['versionCode'] = versionCode.toString()
    // write
    def outStream = new FileOutputStream(versionFile)
    try {
      version.store(outStream, null)
    } finally {
      stream.close()
    }
  }

  println "version code is now " + versionCode
  return versionCode
}

/**
 * compileSdkVersion, buildToolsVersion, minSdkVersion, targetSdkVersion
 * should be matched with 0-scripts/configure_gradle.py
 */
android {
  ...
  defaultConfig {
    applicationId "..."
    minSdkVersion 19
    targetSdkVersion 20
    versionCode readAndIncrementVersionCode()
    versionName "1.0.0"
    ndk {
      abiFilters "armeabi-v7a", "x86"
    }
  }
  ...
}