Application icon with counter on android

How can I implement counter on application icon on the desktop? (like SMS application s开发者_开发问答hows number of unread messages)

Should I implement widget for the same? Is there any tutorial?

You cannot modify an application icon - the path to icon is stored inside AndroidManifest.xml, both files are signed with your certificate, application cannot write to it's own .apk file. You may try a hack - install one "wrapper" app, and let it install/uninstall bunch of other dummy apps, which will have an icons with different numbers on them. However this will require app install permission, which users will be warned about.

So you have to implement a widget.