buid.gradle

dependencies {
  androidTestCompile 'com.android.support.test.uiautomator:uiautomator-v18:2.1.2'
}

Helpers.java

  public static String findChildElementCDByIndex(int index) {
     BySelector messagesListSelector = By.desc("ListView Recycler");
     uiDevice.wait(Until.hasObject(messagesListSelector),6000);
     UiObject2 messageList = uiDevice.findObject(messagesListSelector);
     messageList.getChildren().get(index).getContentDescription();
  }