Why does getActiveNotifications() return Null? Whats wrong?

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Java

Android

hi guys,
was learning notifications in Android and was wonderring why was this code not working... instead its returning Null?

This code snippet is from my MainActivity ,
NotificationService is my public class that extends NotificationListenerService
i have also made the necessary permissions in the Manifest for my app to watch notifications!

protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

NotificationService ns = new NotificationService();
StatusBarNotification[] sbn = ns.getActiveNotifications();
      
        if (sbn != null)
        	{
        	Log.i("XXXXXX", "Lenght: " + sbn.length);
        	}
        else
        	{
        	Log.i("XXXXXX", "Null" );
        	}
       
    }

I am trying to get the getActiveNotifications() inside the NotificationListenerService to return me an array of the Notifications that are already present in the statusbar before i had launched my app... so after i have launched the app and the OnCreate is fired... i still get Null even though there are 4 current notifications?