Programatically getting the version code of the app that is in play store

My android app is published in google play store. I want to do,

1. User get notified when there is new version of app.
2. User must get notified when they are using an older version of app.

The problem I face is,

1. If the user turns off automatic check for update option in google play store, they no longer get notified by the default option.
2. If my user using the older version of my app, it will create problem for me in data management.(conflict problem etc.,)

So what i want is, the user opens my app, checks for the current version code of the app and compare with version code of the app that is in google play store.

I find it difficult to get the version code of the app that is in play store.

I tried following links to get the version code of the app on google play store but of not help.

SO question

https://code.google.com/p/android-market-api/

[How to allow users to check for the latest app version from inside the app?

please help..

How can i programmatically get the version code of the app that is on play store.

Or is there any way that by which I can manually trigger the default built-in event as handled by google play services?

why don't you save your latest version in a google document on google drive and from your application read that value?

Here is the api