MainActivity.java

package com.onesignal.example;

import android.app.Activity;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.widget.TextView;

import com.onesignal.OneSignal;

public class MainActivity extends AppCompatActivity {

   private static Activity currentActivity;
   
   @Override
   protected void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);
      setContentView(R.layout.activity_main);

      OneSignal.idsAvailable(new OneSignal.IdsAvailableHandler() {
         @Override
         public void idsAvailable(String userId, String registrationId) {
            String text = "OneSignal UserID:\n" + userId + "\n\n";

            if (registrationId != null)
               text += "Google Registration Id:\n" + registrationId;
            else
               text += "Google Registration Id:\nCould not subscribe for push";

            TextView textView = (TextView)findViewById(R.id.debug_view);
            textView.setText(text);
         }
      });
   }
}