Numberpicker is a project mainly written in ..., it's free.
Example source of an Android number picker widget
This project contains a working example of a number picker widget for use in Android applications. In addition to the basic widget included in this project is a sample preference dialog that contains the number picker widget. All source code is licensed under the Apache 2.0 License. If you come across issues with the provided code you can file an issue on the Github project page.
The number picker preference uses a few attributes defined in the res/values/attrs.xml file.
In the number picker preference Java class it references the namespace defined in the attrs.xml file.
You'll notice in the res/xml/preferences.xml file in the top level element there's a namespace defined to allow easy use of properties to set max range and min range as well as the default value.