code: private void showPopup() {
  
          updateFromTextBox(true);
          m_box.setPreventShowError(true);
          m_popup.showRelativeTo(m_box);
          if (m_previewHandlerRegistration != null) {
              m_previewHandlerRegistration.removeHandler();
          }
          m_previewHandlerRegistration = Event.addNativePreviewHandler(new CloseEventPreviewHandler());
      }
docs: Shows the date picker popup.<p>