Communication between an Android App and Unity

Introduction

This tutorial shows how to have an android app communicating with an android unity application. It also shows how to communicate between the android java app default code and unity. I had to do such a thing a year ago for one of my teacher that wanted to process data from an external accelerometer directly into unity. He already had an custom android app he made, that can receive these data but no way to send them to a unity game.

I'll assume you already made some android app. For simplification, I won't speak about in default android app creation but just tell you what you need to know to get this done.

How to send information between two Android app

Sending App

There is a simple way to send data from a standard app to another one and it's called a Service. Basically, a service is something inside an app that can broadcast data to any other app that is configured to listen to it. It's a standard android class coming from android.app.Service that can be derived to be used in your app.

Let's have a look on how to that:

• First of all, create a new class inside your sending app, deriving from android.app.Service. This class is the service that will send an Intent to the others apps.
• Now you have to make your service running inside your app. To do so, you can start the service in any Activity simply by using startService(new Intent(this, MyService.class)); where MyService is the name I called my new service derived class.
• When you start it, a new instance of the service is created and directly call its onStart method.
  

Here's an example of a really simple service, using an Handler and sending data each second. All instructions are commented for you to understand how it works:

• You must now modify the AndroidManifest.xml file to let Android know this app has a service in it, otherwise it won't work. So you just have to add this line under the <application> section:

Receiving App

We will see now how to receive the data our sender sends us. As this receiver is made for Unity, it has no activity, and work as a plugin for Unity. 

That's what you must do:

• Create a new android app without any activity
• Make a derived class of android.content.BroadcastReceiver

Here's an example code that explains the nexts parts:

• Compile it as a .jar file. Using Eclipse you can do it trhough Eclipse -> File -> Export -> Java -> Jar File, press next, check your project, uncheck all boxes in the right panel, uncheck jar compression, choose a destination file and press done.

Make Unity use our Java Receiver plugin

Importing the plugin

Unity has been made to be able to use external library in a very simple way.

• Create this hierarchy of folders using the default Asset folder: Assets/Plugins/Android/ 
• Move your .jar file in it

Now, we have to modify the AndroidManifest.xml Unity uses to add some specifications for our receiver plugin to work properly. The easiest way to get this file is to build our Unity project to run on Android. When we build it, Unity create a manifest during compilation, that can be found in the Temp folder of our project. Copy it and move it next to the .jar file in the Android folder.

• Modify the manifest by adding these lines under the <application> section:
  

After <receiver android::name=... you have to add the exact and full location of your Receiver class inside your plugin package. And after <action android::name=... comes the name of the Intent you want to listen at. It must be the same as what you wrote in the Sender in the sendIntent.setAction(...) method.

Using our plugin

Everything is set up now for us to be able to receive data of an other app inside a Unity application. We just have to see now how to use it in a Unity Script:

We're done ! I hope you get all the necessary information to have this working for you. Don't hesitate to ask me if you have any questions or problems. I'll be very happy to help you !

I would like to thank Simon Philippe, a friend of mine, for having worked with me on this code.

As usual, excuse me for all my English mistakes, I'm not a native speaker.