Identifying App Installations

In the Android group, from time to time we hear complaints from developers about problems they’re having coming up with reliable, stable, unique device identifiers. This worries us, because we think that tracking such identifiers isn’t a good idea, and that there are better ways to achieve developers’ goals.

Tracking Installations

It is very common, and perfectly reasonable, for a developer to want to track individual installations of their apps. It sounds plausible just to call TelephonyManager.getDeviceId() and use that value to identify the installation. There are problems with this: First, it doesn’t work reliably (see below). Second, when it does work, that value survives device wipes (“Factory resets”) and thus you could end up making a nasty mistake when one of your customers wipes their device and passes it on to another person.

To track installations, you could for example use a UUID as an identifier, and simply create a new one the first time an app runs after installation. Here is a sketch of a class named “Installation” with one static method Installation.id(Context context). You could imagine writing more installation-specific data into the INSTALLATION file.

public class Installation {

    private static String sID = null;

    private static final String INSTALLATION = "INSTALLATION";

    public synchronized static String id(Context context) {

        if (sID == null) {  

            File installation = new File(context.getFilesDir(), INSTALLATION);

            try {

                if (!installation.exists())

                    writeInstallationFile(installation);

                sID = readInstallationFile(installation);

            } catch (Exception e) {

                throw new RuntimeException(e);

            }

        }

        return sID;

    }

    private static String readInstallationFile(File installation) throws IOException {

        RandomAccessFile f = new RandomAccessFile(installation, "r");

        byte[] bytes = new byte[(int) f.length()];

        f.readFully(bytes);

        f.close();

        return new String(bytes);

    }

    private static void writeInstallationFile(File installation) throws IOException {

        FileOutputStream out = new FileOutputStream(installation);

        String id = UUID.randomUUID().toString();

        out.write(id.getBytes());

        out.close();

    }

}

Identifying Devices

Suppose you feel that for the needs of your application, you need an actual hardware device identifier. This turns out to be a tricky problem.

In the past, when every Android device was a phone, things were simpler: TelephonyManager.getDeviceId() is required to return (depending on the network technology) the IMEI, MEID, or ESN of the phone, which is unique to that piece of hardware

Read more: Android developers

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