Intent within onUtteranceCompleted method not working

Question

I am trying to implement an intent to take the user back to the home screen once the TextToSpeech function completes, but it isn't working, and I'm not sure why. Here is my code:

public void playText(){     
    String text = typeNewMessageEditText.getText().toString();
    HashMap<String, String> myHashRender = new HashMap<String, String>();
    myHashRender.put(TextToSpeech.Engine.KEY_PARAM_UTTERANCE_ID, "completed");
    tts.speak(text, TextToSpeech.QUEUE_FLUSH, myHashRender);        
}


@Override
public void onUtteranceCompleted(String utteranceId) {
    if (utteranceId.equals("completed")){   
                Intent displayMainActivity = new Intent (this, MainActivity.class);
                startActivity(displayMainActivity);
    }   
}