Re: callback between classes

markspace <>
Fri, 12 Nov 2010 08:59:40 -0800
On 11/12/2010 3:44 AM, a wrote:


I have 2 classes. The CatContainer extends the HorizontalPanel. The
CatContainer should be updated when the CatWidget receives updated data
database by GWT RPC.
How can I implement the update of the CatContainer?

As mentioned, MVC will help you out here. The idea is to introduce a
third object, the controller, which knows about both objects and can
bind them at run time.

public class InitializationController {

  public void init() {
    CatContainer model = new CatContainer();
    CatWidget view = new CatWidget();
    model.addChangeListener( view );

class CatContainer extends HorizontalPanel{
private CatWidget catWidget=new CatWidget(1);

  private ModelObserver view;

  public void addChangeListener( ModelObserver obs ) {
    view = obs;

//how can I implement the following to update the GUI?
catWidget.refresh( new CallBackFunc()

    final CatContainer localModel = CatContainer.this;

//Update GUI

    if( localModel.view != null) {



class CatWidget

     implements ModelObserver

private data;

void refresh()
//Call GWT async to retrieve data from database, and update the data.


public interface ModelObserver {
   void refersh();

Nothing here was compiled, double check my syntax.

I don't like the comment you have in "CatWidget". The view should not
know about any database. It should have a simple interface for a model
and that's it. Update the model from the database, then inform the view
that the model has changed. However, I'll leave design issues like that
one to you.

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