Change action when pressing a virtual buttom

Hello. I'm trying to show a toast message (Android) when the user "press" a virtual button. I've been reading this post https://developer.vuforia.com/resources/dev-guide/open-web-site-and-display-toast-target-detection but I can´t do it. When I follow the instructions of that post I get an error in my Android project, here...:

public void displayMessage(String text)

    {

                 android.os.Message message = new android.os.Message();

                 message.obj = text;

                 mainActivityHandler.sendMessage(message); // Here is the error: The method sendMessage(Message) in the type Handler is not applicable for the arguments (Message)

    }

I've done everything as explained in the post, but doint it in the VirtualButtons sample instead of the ImageTargets sample, but I suppose that change shouldn't be a problem. 

Thank you very much