How to autoupdate android app without playstore? Like Facebook app or any Contest app

If you would like to check if you app has updates (without interacting with Google Play), you'd have to poll a server (providing your current version) and let the server check if there is a newer version available. If that is the case, let the server respond with a changelog and an url to the newer version.

Luckily, there are libraries to do this:

• AppUpdater. Android Library that checks for updates on your own server (or Google Play, Github, etc). Great documentation. This library notifies your apps' updates by showing a Material dialog, Snackbar or notification.
• Android Auto Update. Chinese library, but should do the trick, one of the most popular libraries to do this, but this can be just because Google Play is not available in China.
• AppUpdateChecker A simple non-Market way to keep your app updated. All it requires to set up is a URL pointing to a JSON document describing your app's changes.
• Auto Updater This project allows to automatically update a running APK application using a private update server (see apk-updater) instead of Google Play updater. Also comes with a server script.
• SmartUpdates. Older library, but instructions in English and also provides a server script.
• WVersionManager. Checks for updates, but actual update has to be downloaded from the Play Store.