code: @SuppressWarnings("deprecation")
      public static void activateApp(Context context, String applicationId) {
          if (context == null || applicationId == null) {
              throw new IllegalArgumentException("Both context and applicationId must be non-null");
          }
  
          if ((context instanceof Activity)) {
              setSourceApplication((Activity) context);
          } else {
            // If context is not an Activity, we cannot get intent nor calling activity.
            resetSourceApplication();
            Log.d(AppEventsLogger.class.getName(),
                "To set source application the context of activateApp must be an instance of Activity");
          }
  
          // activateApp supercedes publishInstall in the public API, so we need to explicitly invoke it, since the server
          // can't reliably infer install state for all conditions of an app activate.
          Settings.publishInstallAsync(context, applicationId, null);
  
          final AppEventsLogger logger = new AppEventsLogger(context, applicationId, null);
          final long eventTime = System.currentTimeMillis();
          final String sourceApplicationInfo = getSourceApplication();
          backgroundExecutor.execute(new Runnable() {
              @Override
              public void run() {
                  logger.logAppSessionResumeEvent(eventTime, sourceApplicationInfo);
              }
          });
      }
docs: Notifies the events system that the app has launched & logs an activatedApp event.  Should be called whenever
  your app becomes active, typically in the onResume() method of each long-running Activity of your app.
  
  @param context       Used to access the attributionId for non-authenticated users.
  @param applicationId The specific applicationId to report the activation for.