Developing two android apps and communicating between two
You cannot directly access methods of Activity in different app.
Broadcast would work but if you want more control (i.e. invoke remote methods) consider binding to a remote service in the other app or use Messenger and handler to communicate.
Here is a short tutorial on inter-app communication
You can't share methods and code segments between different applications, but you can use intents to send data bundles back and forth, check this similar question: