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So I'm trying to implement gcm or my app with the help of
this documentation
. However, when trying to launch my application, I get following error:
java.lang.RuntimeException: An error occured while executing doInBackground()
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.pm.PackageManager android.content.Context.getPackageManager()' on a null object reference
Here is the code in question:
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
throw new RuntimeException("Could not get package name: " + e);
What is my mistake here?
EDIT: Where I'm using "getAppVersion":
private String getRegistrationId(Context context) {
final SharedPreferences prefs = getGCMPreferences(context);
String registrationId = prefs.getString(PROPERTY_REG_ID, "");
if (registrationId.isEmpty()) {
Log.i(TAGD, "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(TAGD, "App version changed.");
return "";
return registrationId;
private void storeRegistrationId(Context context, String regId) {
final SharedPreferences prefs = getGCMPreferences(context);
int appVersion = getAppVersion(context);
Log.i(TAGD, "Saving regId on app version " + appVersion);
SharedPreferences.Editor editor = prefs.edit();
editor.putString(PROPERTY_REG_ID, regId);
editor.putInt(PROPERTY_APP_VERSION, appVersion);
editor.apply();
Where I start getRegistrationId:
in the onCreate method,
if (checkPlayServices()) {
gcm = GoogleCloudMessaging.getInstance(this);
regid = getRegistrationId(context);
if (regid.isEmpty()) {
registerInBackground();
} else {
Log.v(TAGD, "No valid GPS APK found.");
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