Hostinicon
GET HOSTING FROM $3.95/MO PLUS A FREE YEAR ON TUTS+ (RRP $180). HURRY OFFER LIMITED. Check it out
Advertisement

Reading NFC Tags with Android

by
Gift

Get a free year on Tuts+ this month when you purchase a Siteground hosting plan from $3.95/mo

Are you curious about what NFC is and how it can be integrated into your own Android applications? This tutorial will quickly introduce you to the topic before diving in and teaching you how to build a simple NFC reader app!


What is NFC?

NFC is the abbreviation for Near Field Communication. It is the international standard for contactless exchange of data. In contrast to a large range of other technologies, such as wireless LAN and Bluetooth, the maximum distance of two devices is 10cm. The development of the standard started in 2002 by NXP Semiconductors and Sony. The NFC Forum, a consortium of over 170 companies and members, which included Mastercard, NXP, Nokia, Samsung, Intel, and Google, has been designing new specifications since 2004.

There are various possibilities for NFC use with mobile devices; for example, paperless tickets, access controls, cashless payments, and car keys. With the help of NFC tags you can control your phone and change settings. Data can be exchanged simply by holding two devices next to each other.

In this tutorial I want to explain how to implement NFC with the Android SDK, which pitfalls exist, and what to keep in mind. We will create an app step by step, which can read the content of NFC tags supporting NDEF.


NFC Technologies

There are a variety of NFC tags that can be read with a smartphone. The spectrum ranges from simple stickers and key rings to complex cards with integrated cryptographic hardware. Tags also differ in their chip technology. The most important is NDEF, which is supported by most tags. In addidition, Mifare should be mentioned as it is the most used contactless chip technology worldwide. Some tags can be read and written, while others are read-only or encrypted.

Only the NFC Data Exchange Format (NDEF) is discussed in this tutorial.

girogo-card

Adding NFC Support in an App

We start with a new project and a blank activity. It is important to select a minimum SDK version of level 10, because NFC is only supported after Android 2.3.3. Remember to choose your own package name. I've chosen net.vrallev.android.nfc.demo, because vrallev.net is the domain of my website and the other part refers to the topic of this application.

The default layout generated by Eclipse is almost sufficient for us. I've only added an ID to the TextView and changed the text.

To get access to the NFC hardware, you have to apply for permission in the manifest. If the app won't work without NFC, you can specify the condition with the uses-feature tag. If NFC is required, the app can't be installed on devices without it and Google Play will only display your app to users who own a NFC device.

The MainActivity should only consist of the onCreate() method. You can interact with the hardware via the NfcAdapter class. It is important to find out whether the NfcAdapter is null. In this case, the Android device does not support NFC.

If we start our app now, we can see the text whether NFC is enabled or disabled.

How to Filter for NFC Tags

We have our sample app and want to receive a notification from the system when we attach an NFC tag to the device. As usual, Android uses its Intent system to deliver tags to the apps. If multiple apps can handle the Intent, the activity chooser gets displayed and the user can decide which app will be opened. Opening URLs or sharing information is handled the same way.


NFC Intent Filter

There are three different filters for tags:

  1. ACTION_NDEF_DISCOVERED
  2. ACTION_TECH_DISCOVERED
  3. ACTION_TAG_DISCOVERED

The list is sorted from the highest to the lowest priority.

Now what happens when a tag is attached to the smartphone? If the system detects a tag with NDEF support, an Intent is triggered. An ACTION_TECH_DISCOVERED Intent is triggered if no Activity from any app is registered for the NDEF Intent or if the tag does not support NDEF. If again no app is found for the Intent or the chip technology could not be detected, then a ACTION_TAG_DISCOVERED Intent is fired. The following graphic shows the process:

nfc tag dispatch

In summary this means that each app needs to filter after the Intent with the highest priority. In our case, this is the NDEF Intent. We implement the ACTION_TECH_DISCOVERED Intent first to highlight the difference between priorities.


Tech Discovered Intent

We must specify the technology we are interested in. For this purpose, we create a subfolder called xml in the res folder. In this folder we create the file nfc_tech_filter.xml, in which we specify the technologies.

Now we must create an IntentFilter in the manifest, and the app will be started when we attach a tag.

If no other app is registered for this Intent, our Activity will start immediately. On my device, however, other apps are installed, so the activity chooser gets displayed.

screenshot

NDEF Discovered Intent

As I mentioned before, the Tech Discovered Intent has the second highest priority. However, since our app will support only NDEF, we can use the NDEF Discovered Intent instead, which has a higher priority. We can delete the technology list again and replace the IntentFilter with the following one.

When we attach the tag now, the app will be started like before. There is a difference for me, however. The activity chooser does not appear and the app starts immediately, because the NDEF Intent has a higher priority and the other apps only registered for the lower priorities. That's exactly what we want.


Foreground Dispatch

Note that one problem remains. When our app is already opened and we attach the tag again, the app is opened a second time instead of delivering the tag directly. This is not our intended behavior. You can bypass the problem by using a Foreground Dispatch.

Instead of the system having distributed the Intent, you can register your Activity to receive the tag directly. This is important for a particular workflow, where it makes no sense to open another app.

I've inserted the explanations at the appropriate places in the code.

Now, when you attach a tag and our app is already opened, onNewIntent is called and no new Activity is created.


Reading Data From an NDEF Tag

The last step is to read the data from the tag. The explanations are inserted at the appropriate places in the code once again. The NdefReaderTask is a private inner class.

The app now successfully reads the content.

screen

Useful Apps

To check whether data is read and written properly, I personally like to use following apps:

  • NFC TagInfo by NFC Research Lab for reading data
  • TagInfo by NXP SEMICONDUCTORS for reading data
  • TagWriter by NXP SEMICONDUCTORS for writing data

Conclusion

In this tutorial I have shown you how the data from a NDEF tag can be extracted. You could expand the example to other mime types and chip technologies; a feature to write data would be useful as well. The first step to work with NFC was made. However, the Android SDK offers much more possibilities, such as an easy exchange of data (called Android Beam).


About the Author

Ralf Wondratschek is a computer science student from Germany. In addition to his studies, Ralf works as a freelancer in the field of mobile computing. In the last few years he has worked with Java, XML, HTML, JSP, JSF, Eclipse, Google App Engine, and of course Android. He has published two Android apps to date which can be found here.

You can find out more about the author’s work on his homepage vrallev.net.


Sources

http://www.nfc-forum.org/home/n-mark.jpg

http://commons.wikimedia.org/wiki/File%3A%C3%9Cberlagert.jpg

http://developer.android.com/images/nfc_tag_dispatch.png


Advertisement