code: protected void onSelectedItemsChanged() {
          final Collection<ItemT> selectedItems = getSelectedItems();
          if (selectedItems.isEmpty()) {
              anchorLabel();
              getInputWidget().setText("");
          } else {
              getInputWidget().setText(getItemPrinter().printCollection(selectedItems));
              floatLabel();
          }
          if (itemPickerListener != null) itemPickerListener.onSelectionChanged(this, selectedItems);
      }
docs: Refreshes the widget state when the selection changes