code: private void initializeForTouchDevice() {
  		logger.log(Level.FINE, "ZoomControl -> initializeForTouchDevice()");
  		// Add touch handlers to the zoom in button:
  		zoomInElement.addDomHandler(new TouchStartHandler() {
  
  			@Override
  			public void onTouchStart(TouchStartEvent event) {
  				event.stopPropagation();
  				event.preventDefault();
  
  				logger.log(Level.FINE, "ZoomControl -> zoomInElement onTouchStart()");
  				ViewPort viewPort = mapPresenter.getViewPort();
  				int index = viewPort.getResolutionIndex(viewPort.getResolution());
  
  				if (index < viewPort.getResolutionCount() - 1) {
  					viewPort.applyResolution(viewPort.getResolution(index + 1));
  					viewPort.getPosition();
  				}
  			}
  		}, TouchStartEvent.getType());
  
  		// Add touch handlers to the zoom out button:
  		zoomOutElement.addDomHandler(new TouchStartHandler() {
  
  			@Override
  			public void onTouchStart(TouchStartEvent event) {
  				logger.log(Level.FINE, "zoomOutElement -> zoomInElement onTouchStart()");
  				event.stopPropagation();
  				event.preventDefault();
  
  				ViewPort viewPort = mapPresenter.getViewPort();
  				int index = viewPort.getResolutionIndex(viewPort.getResolution());
  
  				if (index > 0) {
  					viewPort.applyResolution(viewPort.getResolution(index - 1));
  				}
  			}
  		}, TouchStartEvent.getType());
  	}
docs: Initialize handlers for mobile devices.