Question

Although I try other answer about this problem, it can’t be solved.
Sender ID is correct, permissions are added, API key is true.

I use this post for creating the project:
http://developer.android.com/guide/google/gcm/gs.html#server-app

    GCMRegistrar.checkDevice(this);
    GCMRegistrar.checkManifest(this);
    String regId = GCMRegistrar.getRegistrationId(this);
    if (regId.equals("")) {
      GCMRegistrar.register(this, SENDER_ID);
      regId = GCMRegistrar.getRegistrationId(this);
    } else {
      Log.v(TAG, "Already registered");
    }
    String did = getDeviceID();

it returns empty string.

Answer 1

Do you have GCMIntentService defined correctly at the root package of your app?

<receiver android:name="com.google.android.gcm.GCMBroadcastReceiver" android:permission="com.google.android.c2dm.permission.SEND" >

  <intent-filter>
    <action android:name="com.google.android.c2dm.intent.RECEIVE" />
    <action android:name="com.google.android.c2dm.intent.REGISTRATION" />
    <category android:name="my_app_package" />
  </intent-filter>
</receiver>

Make sure that "my_app_package" is identical to the main package of your app, or your id will return an empty string.

Also notice that

    GCMRegistrar.register(this, "...");

is asynchronous. Therefore, calling GCMRegistrar.getRegistrationId(this) immediately after that is not reliable, so you should avoid it.

The id will arrive via broadcast callback to your GCMIntentService, as a part of the registration procedure. from there you can then store the gcm/fcm key anywhere you like, and use it in other parts of the application (usually on the server).