16 Oct 2015

Android Programming with Eclipse & Java - Tutorial

In an earlier post we had shown how a generic XMPP chat client (Xabber), running on an Android machine could be used as an IOT component to transmit data and commands, through a publicly hosted XMPP chat server, that can be stored or executed on a distant machine that hosts a python chatbot listener program.

However for any meaningful IOT task to be performed, we need a custom built XMPP chat client that will pick up up data from sensors and transmit it to the listener program. This would be a rather minimal XMPP client, without the bells and whistles required for a full fledged interactive chat client. All that it needs to do is to connect to a XMPP server, login with its userid/password credentials and transmit a IM message to the chatbot listener. Such a program for the Android program needs to be written in Java but BEFORE you begin typing "public static void main(string args) ...etc" you need to get your machine ready for Android programming ...

and believe me, that is not for the faint hearted!

However, don't panic! do not lose heart. I did it and so can you!

There are many tools that will help you build Android apps very quickly using a browser based GUI with drag and drop tools. One such is the AppInventor from MIT for which a decent tutorial is available in the StudyTonight website. Using this, you can build nice, quirky apps that will amuse your friends and give you bragging rights for being an Android developer. But these are just for toys. If you want do serious stuff, you need to go through what we are about to describe in this post.

First question, would you want to work in Windows or Linux ?

Most hardcore application developers, particularly the geeky nerds, prefer working with Linux. My machine has dual boot configuration with one Windows 7 partition and one Ubuntu 14.04 partition and I do most of my development in Ubuntu. However from Windows 8 onwards, dual boot is very difficult if not impossible. So the only option would be download the Oracle VirtualBox software into your Windows machine and install a free Ubuntu image by following instructions given on this page.

All this assumes that you want to develop on Linux. If you prefer the Windows platform then this post may not be relevant for you, except for pure academic interest.

The next decision is about which IDE ( Integrated Development Environment ) to use. Google offers the Android Studio that you can download and then you can Build Your First App by following the instructions. I went down this path and built my first HelloWorld program but realized that most people prefer the Eclipse option and so most of the samples and examples are based on Eclipse. Hence I also abandoned the Android Studio and joined the Eclipse bandwagon. Going forward, we shall stick to the Eclipse option.

I had already installed Eclipse v 3.8 on my Ubuntu partition for an earlier Hadoop project and so it was already there on my machine. However you may read about How to Install Latest Eclipse on Ubuntu by searching for the same on Google. Once Eclipse is installed it may be a good idea to write and run a Hello World program in Java/Eclipse. Just to make sure that things are good to go.

Now for the real stuff -- Java for Android on Eclipse!

First make sure that your development environment is adequate, and then set up the Android SDK. There are four tasks here, namely (a) Download the SDK, (b) Install Eclipse -- not necessary if you already have Eclipse, (c) Setup the Android Development Tool Plug In and (d) Create an Android Virtual device for you to test your Android Apps -- all of which are explained in the link given above. This download takes a while, read every screen carefully and generally go with the defaults.

Now you may go over and create your first hello world Android application. Do not forget to check out the various other excellent tutorials on the left side-bar.

If everything goes well, you will see the Android Virtual Device being launched. It will look like any Android phone and you can click on the usual Android buttons and even browse the web or take pictures with it -- if you have configured it correctly. For the Hello World program, the sequence of screens will look like this.





Our application name is HelloWorld0851 ( located in the third row, right side) and when clicked it shows a little fragment of text "Namaskar 0851 Emulator".

If at this point, you go to the Linux terminal and run the command the Android Device Bridge (adb) command  >adb devices.

We will see only one Android Devices Connected to the machine -- this is the Emulator



Now we need to move from the Simulator to some real Android devices and I connect my Motorola Phone and Micromax Xiaomi tablet to the USB ports of the laptop. When connected, these devices show up on the adb command as follows:



The TA is the Motorola device and the 13E is the Micromax device. Now when you execute the HelloWorld program, you will be prompted to choose the device where it will be installed and run.

So are we done ? Well, I wish I could say so ... but NO,  it is not very easy for the external devices to get connected to the Eclipse development environment.

So how do you connect an Android device to the Eclipse Development Environment ?

Step 1 : USB debugging mode.

When an Android device is connected to the USB port of a computer it is usually in the "media mode" that means that you can only transfer files (including .APK ). For serious work, the machine needs to be put in USB debug mode. Usually, the USB debug mode is hidden from lay users and has be discovered and activated and the process is different for each version of Android.

For the Motorola phone  running Android 5.1 you need to go to :
Settings > About Phone > Build Number and press it 7 times.

For the Micromax Tablet running Android 4.4.4 you need to go to
Settings > About Pad > MIUI version and press 7 times

This is "Khulja Sim Sim" to the Alladin's cave of Android development and a new option called Developer Options will appear on Settings menu and within this there will be another option called USB debug mode. Both Developer Options and USB debug mode needs to be activated. When you do this for the first time, there may be a security warning and  you need to accept the warning and allow the process to move forward. Denying the request will put your device in the limbo as far as application development is concerned.

For the specific device that you are using, you will have to Google for the steps involved or arrive their by trial and error!

In many cases, this is adequate. One needs to stop, restart the adb service by simply
>sudo adb kill-server
>sudo adb start-server
and hopefully the device will be detected.

But very often than not, this is not enough. Even after activating USB debug mode, the device may not be recognized. So now

Step 2 : Android-Rules

You need to create a file called 51-android-rules in the /etc/udev/rules.d directory as described in this post How to fix ADB no permissions, and explained in context in Stackoverflow. This will solve the problem for most common Android vendors, including Motorola, but unfortunately that does not include Micromax!

To identify the ID of the USB connected Micromax device, we executed the lsusb command :

This shows the ID of the various devices connected to the USB ports, most of which are recognizable from the descriptions.

For example ID 22b8-2382 is the Motorola Device and it is duly visible in the original file that we downloaded. So the there is a good chance that the unknown device with ID 271-066B must be the Micromax device. So we append on extra dummy line at the bottom of the 51-android-rules file with one extra line

SUBSYSTEM=="usb", ATTRS{idVendor}=="2717", MODE="0666"

and that does the trick! After creating the file with the extra line and executing the commands given in the two posts, both the Android devices are clearly visible with the adb command and are available for testing the application.

Update : My new Micromax Android One running Android 6 was recognised by the Android SDK without any problem. Just set it in USB debugging mode and you are done!

Now we are finally ready!

Go back to Eclipse and run the "MainActivity" java file of the HelloWorld program. There will be a prompt to choose the device which could be any one of the three devices, the emulator, the Motorola phone or the Micromax tablet. Once a physical device is chosen, the application will be installed on the device, started and will also be available like any other downloaded app.

The final hurdle to this happy state of affairs is Android Security does not allow apps to be installed from an unknown source, that is anything other than Google Play. This can be addressed by a simple configuration change that allows App Installs from Unknown Sources.

At the end of all this, we are finally ready to start building a real useful app for the XMPP client. That presents its own set of challenges with the Smack library that connects to the Ignite Openfire server. But that is another post for another day. Keep watching this space!


P.S. If you find this USB debug mode and the Android-Rules to be too much for you, you can always copy the APK file manually into the device while it is connected in the simple media-mode and install it by tapping the file twice in a file browser. See here.

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