Checking for registration ID and registering app

app/src/main/java/com/example/android/sunshine/app/MainActivity.java

@@ -15,8 +15,14 @@
  */
 package com.example.android.sunshine.app;
 
+import android.app.AlertDialog;
+import android.content.Context;
 import android.content.Intent;
+import android.content.SharedPreferences;
+import android.content.pm.PackageInfo;
+import android.content.pm.PackageManager;
 import android.net.Uri;
+import android.os.AsyncTask;
 import android.os.Bundle;
 import android.support.v7.app.ActionBarActivity;
 import android.util.Log;
@@ -26,15 +32,28 @@ import android.view.MenuItem;
 import com.example.android.sunshine.app.sync.SunshineSyncAdapter;
 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;
+import java.util.concurrent.atomic.AtomicInteger;
 
 public class MainActivity extends ActionBarActivity implements ForecastFragment.Callback {
 
     private final String LOG_TAG = MainActivity.class.getSimpleName();
     private static final String DETAILFRAGMENT_TAG = "DFTAG";
     private final static int PLAY_SERVICES_RESOLUTION_REQUEST = 9000;
+    public static final String PROPERTY_REG_ID = "registration_id";
+    private static final String PROPERTY_APP_VERSION = "appVersion";
+
+    /**
+     * Substitute you own sender ID here. This is the project number you got
+     * from the API Console.
+     */
+    String SENDER_ID = "Your-Sender-ID";
 
     private boolean mTwoPane;
     private String mLocation;
+    private GoogleCloudMessaging mGcm;
 
     @Override
     protected void onCreate(Bundle savedInstanceState) {
@@ -66,12 +85,26 @@ public class MainActivity extends ActionBarActivity implements ForecastFragment.
 
         SunshineSyncAdapter.initializeSyncAdapter(this);
 
-        if (!checkPlayServices()) {
+        // If Google Play Services is not available, some features, such as GCM-powered weather
-            // this is where we could either prompt a user that they should install
+        // alerts, will not be available.
-            // the latest version of Google Play Services, or add an error snackbar
+        if (checkPlayServices()) {
-            // that some features won't be available.
+            mGcm = GoogleCloudMessaging.getInstance(this);
-        }
+            String regId = getRegistrationId(this);
 
+            if (SENDER_ID.equals("Your-Sender-ID")) {
+                new AlertDialog.Builder(this)
+                .setTitle("Needs Sender ID")
+                .setMessage("GCM will not function in Sunshine until you replace your Sender ID with a Sender ID from the Google Developers Console.")
+                .setPositiveButton(android.R.string.ok, null)
+                .create().show();
+            } else if (regId.isEmpty()) {
+                registerInBackground(this);
+            }
+        } else {
+            Log.i(LOG_TAG, "No valid Google Play Services APK. Weather alerts will be disabled.");
+            // Store regID as null
+            storeRegistrationId(this, null);
+        }
     }
 
     @Override
@@ -162,4 +195,113 @@ public class MainActivity extends ActionBarActivity implements ForecastFragment.
         }
         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.
+     */
+    private String getRegistrationId(Context context) {
+        final SharedPreferences prefs = getGCMPreferences(context);
+        String registrationId = prefs.getString(PROPERTY_REG_ID, "");
+        if (registrationId.isEmpty()) {
+            Log.i(LOG_TAG, "GCM Registration not found.");
+            return "";
+        }
+
+        // Check if app was updated; if so, it must clear the registration ID
+        // since the existing registration ID 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) {
+            Log.i(LOG_TAG, "App version changed.");
+            return "";
+        }
+        return registrationId;
+    }
+
+    /**
+     * @return Application's {@code SharedPreferences}.
+     */
+    private SharedPreferences getGCMPreferences(Context context) {
+        // Sunshine persists the registration ID in shared preferences, but
+        // how you store the registration ID in your app is up to you. Just make sure
+        // that it is private!
+        return getSharedPreferences(MainActivity.class.getSimpleName(), Context.MODE_PRIVATE);
+    }
+
+    /**
+     * @return Application's version code from the {@code PackageManager}.
+     */
+    private static int getAppVersion(Context context) {
+        try {
+            PackageInfo packageInfo = context.getPackageManager()
+                    .getPackageInfo(context.getPackageName(), 0);
+            return packageInfo.versionCode;
+        } catch (PackageManager.NameNotFoundException e) {
+            // Should never happen. WHAT DID YOU DO?!?!
+            throw new RuntimeException("Could not get package name: " + e);
+        }
+    }
+
+    /**
+     * Registers the application with GCM servers asynchronously.
+     * <p>
+     * Stores the registration ID and app versionCode in the application's
+     * shared preferences.
+     */
+    private void registerInBackground(final Context context) {
+        new AsyncTask<Void, Void, Void>() {
+            @Override
+            protected Void doInBackground(Void... params) {
+                String msg = "";
+                try {
+                    if (mGcm == null) {
+                        mGcm = GoogleCloudMessaging.getInstance(context);
+                    }
+                    String regId = mGcm.register(SENDER_ID);
+                    msg = "Device registered, registration ID=" + regId;
+
+                    // You should send the registration ID to your server over HTTP,
+                    // so it can use GCM/HTTP or CCS to send messages to your app.
+                    // The request to your server should be authenticated if your app
+                    // is using accounts.
+                    //sendRegistrationIdToBackend();
+                    // For this demo: we don't need to send it because the device
+                    // will send upstream messages to a server that echo back the
+                    // message using the 'from' address in the message.
+
+                    // Persist the registration ID - no need to register again.
+                    storeRegistrationId(context, regId);
+                } catch (IOException ex) {
+                    msg = "Error :" + ex.getMessage();
+                    // TODO(joannasmith): If there is an error, don't just keep trying to register.
+                    // Require the user to click a button again, or perform
+                    // exponential back-off.
+                }
+                return null;
+            }
+        }.execute(null, null, null);
+    }
+
+    /**
+     * 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);
+        Log.i(LOG_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();
+    }
 }