GCMHelper improvements

GCMHelper.java

import android.app.Activity;
import android.content.Context;
import android.content.SharedPreferences;
import android.content.pm.PackageInfo;
import android.content.pm.PackageManager;
import android.os.AsyncTask;

import com.google.android.gms.common.ConnectionResult;
import com.google.android.gms.common.GooglePlayServicesUtil;
import com.google.android.gms.gcm.GoogleCloudMessaging;

import java.io.IOException;

/**
 * Created by Aleksandr Beshkenadze <beshkenadze@gmail.com> on 04.12.13.
 */
public class GCMHelper {
    private final static int PLAY_SERVICES_RESOLUTION_REQUEST = 9000;
    public static final String EXTRA_MESSAGE = "message";
    public static final String PROPERTY_REG_ID = "registration_id";
    private static final String PROPERTY_APP_VERSION = "appVersion";

    public static final String SENDER_ID = BuildConfig.GCM_SENDER_ID;
    private static final String TAG = "GCM";
    private static volatile GCMHelper instance;
    private final Context context;
    private GoogleCloudMessaging gcm;
    private String regId;

    private GCMHelper(Context context) {
        this.context = context;
    }

    public static GCMHelper getInstance(Context context) {
        if (instance == null) {
            synchronized (GCMHelper.class) {
                if (instance == null) {
                    instance = new GCMHelper(context);
                }
            }
        }

        return instance;
    }


    /**
     * Check the device to make sure it has the Google Play Services APK. If
     * it doesn't, display a dialog that allows users to download the APK from
     * the Google Play Store or enable it in the device's system settings.
     */
    public static boolean checkPlayServices(Activity activity) {
        int resultCode = GooglePlayServicesUtil.isGooglePlayServicesAvailable(activity);
        if (resultCode != ConnectionResult.SUCCESS) {
            if (GooglePlayServicesUtil.isUserRecoverableError(resultCode)) {
                GooglePlayServicesUtil.getErrorDialog(resultCode, activity,
                        PLAY_SERVICES_RESOLUTION_REQUEST).show();
            } else {
                L.i(TAG, "This device is not supported.");
            }
            return false;
        }
        return true;
    }

    /**
     * Gets the current registration ID for application on GCM service.
     * <p/>
     * If result is empty, the app needs to register.
     *
     * @return registration ID, or empty string if there is no existing
     * registration ID.
     */
    public static String getRegistrationId(Context context) {
        final SharedPreferences prefs = getGCMPreferences(context);
        String registrationId = prefs.getString(PROPERTY_REG_ID, "");
        if (registrationId.isEmpty()) {
            L.i(TAG, "Registration not found.");
            return "";
        }
        // Check if app was updated; if so, it must clear the registration ID
        // since the existing regID is not guaranteed to work with the new
        // app version.
        int registeredVersion = prefs.getInt(PROPERTY_APP_VERSION, Integer.MIN_VALUE);
        int currentVersion = getAppVersion(context);
        if (registeredVersion != currentVersion) {
            L.i(TAG, "App version changed.");
            return "";
        }
        return registrationId;
    }

    /**
     * @return Application's {@code SharedPreferences}.
     */
    public static SharedPreferences getGCMPreferences(Context context) {
        // This sample app persists the registration ID in shared preferences, but
        // how you store the regID in your app is up to you.
        return context.getSharedPreferences(context.getPackageName(),
                Context.MODE_PRIVATE);
    }

    /**
     * @return Application's version code from the {@code PackageManager}.
     */
    public static int getAppVersion(Context context) {
        try {
            PackageManager pm = context.getPackageManager();
            if (pm != null) {
                PackageInfo packageInfo = pm.getPackageInfo(context.getPackageName(), 0);
                return packageInfo.versionCode;
            }
        } catch (PackageManager.NameNotFoundException e) {
            // should never happen
            throw new RuntimeException("Could not get package name: " + e);
        }
        return -1;
    }

    class RegisterGCMAsyncTask extends AsyncTask<Void, String, String> {

        @Override
        protected String doInBackground(Void... params) {
            try {
                if (gcm == null) {
                    gcm = GoogleCloudMessaging.getInstance(context);
                }
                regId = gcm.register(SENDER_ID);
                storeRegistrationId(context, regId);
            } catch (IOException ex) {
                L.e(TAG, ex.toString());
            }
            return regId;
        }

        /**
         * Stores the registration ID and app versionCode in the application's
         * {@code SharedPreferences}.
         *
         * @param context application's context.
         * @param regId   registration ID
         */
        private void storeRegistrationId(Context context, String regId) {
            final SharedPreferences prefs = getGCMPreferences(context);
            int appVersion = getAppVersion(context);
            L.i(TAG, "Saving regId on app version " + appVersion);
            SharedPreferences.Editor editor = prefs.edit();
            editor.putString(PROPERTY_REG_ID, regId);
            editor.putInt(PROPERTY_APP_VERSION, appVersion);
            editor.commit();
        }

        @Override
        protected void onPostExecute(String msg) {
            super.onPostExecute(msg);
        }
    }
}