How to zoom in out with the Google cardboard

Question

I'm working in a project with the cardboard from Google. I'm asking if there is someone who have the possibility to help with understanding and creating a script for the zoom in and out with the magnet tool on the cardboard. Thanks a lot for your help.

Answer 1

 Used this code 
@Override
public void onCardboardTrigger() {
if (xyz) {
 //Create a function 
zoom();
    ...
} else {

}
// Always give user feedback
  mVibrator.vibrate(50);
}