Flow Synchronization

Example: Root and Child Restaurent List (Java)

With example I hava couple of simple screens. The root is a list of restaurents. To edit the list you click on the restaurent entry to edit the details. If you change the name, then the list needs to update itself, both in the contents of the name and also to preserve alphabetical order.

The restaurent class is so boring I won't repeat it here. There are just string fields corresponding to the fields on the UI and the attendent getters and setters. Not much of a class, but it's not the focus of this discussion so I can permit its sad, pathetic existance.

The form that edits the restaurent details is also rather simple. I have a single flobal update listener that I attach to each field, so any change in a field causes a global refresh of the underlying domain object and the form - this is coarse-grained synchronization.

class RestaurentForm…

  public class FieldListener extends GlobalListener {
     void update() {
         save();
         load();
     }
  }
  private void load() {
      nameField.setText(model.getName());
      placeField.setText(model.getPlace());
      favoritesField.setText(model.getFavorites());
      directionsField.setText(model.getDirections());
  }
   private void save() {
       model.setName(nameField.getText());
       model.setPlace(placeField.getText());
       model.setFavorites(favoritesField.getText());
       model.setDirections(directionsField.getText());
   }

The restaurent list needs to be updated at two points, on initial creation of the form and whenever a child window closes. I put the code to update the list in a method.

class RestaurentListForm...

  void load() {
      sortModel();
      list.setListData(getRestaurentNames());
  }

  private String[] getRestaurentNames() {
      String[] result = new String[model.size()];
      int i = 0;
      for (Restaurent r : model) result[i++] = r.getName();
      return result;
  }

  private void sortModel() {
      Collections.sort(model, new Comparator<Restaurent>() {
          public int compare(Restaurent r1, Restaurent r2) {
              return r1.getName().compareTo(r2.getName());
          }
      });
  }

I then call it from the constructor of the form and from an action listener attached to the edit button.

class RestaurentListForm...

  public RestaurentListForm(List<Restaurent> model) {
      this.model = model;
      buildForm();
      load();
      window.pack();
      window.setVisible(true);
  }

private class EditActionListener implements ActionListener {
    public void actionPerformed(ActionEvent e) {
        new RestaurentForm(window, selectedRestaurent());
        load();
    }
}

private class RestaurentListModel extends AbstractListModel {
    private List<Restaurent> data;
    public RestaurentListModel(List<Restaurent> data) {
        this.data = data;
    }
    public int getSize() {
        return data.size();
    }
    public Object getElementAt(int index) {
        return data.get(index).getName();
    }
}