Build.xml for my existing android project

Hi friends am just stuck up with this issue I have a requirement for a project which has to support multiple versioning of the application.. i searched everywhere and found that we can do that by using ant script ....i have no idea how to make a build.xml in my existing project and how to cha开发者_如何学Gonge my proj .apk file name automatically .... worst part i have to fetch the new name of the apk from another XML file inside my project folder please can anybody help me em running short of time ....