Re: MVC and application state

Philipp <sicsicsic@freesurf.ch> writes:


  (If replying to this post, please do not quote all of it, but
  only small parts you directly refer to [where ?you? does not
  refer to Philipp, but to anyone replying to this post].)

  Usually, the GUI is observing the model via the observer pattern.


  Usually, it would not be part of the GUI, but of the
  application model. Especially, when it usually is ?hidden
  from the user?.

  Swing does not use the original MVC. For example, it uses
  UI-delegates, not controllers and views.

  Here is an example code by me to show how to use the original
  MVC with Swing in Java as truly as possible. But since this
  was my main intention, the code has become larger than
  necessary in Java alone, without this intention.

  As in your question, it keeps a single-bit state.

  The class ?Button1Model? is the application model in this
  case. Some comments refer to the name of Smalltalk messsages
  used in the original MVC, which originated in Smalltalk,
  though the correspondence is not always perfect, because
  Java+Swing is not Smalltalk. For an explanation, see [Burbeck 87]:

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

  From reading the code below, you can learn how ?Button1Model?
  holds a list of its observers and how ?Button1View? registers
  itself with this model and then observes it.

  I am using this program in my class at a point, where control
  statements like ?if? or ?while? have not been introduced yet -
  so all is done without a single ?if? or ?while?.

ButtonModel.java

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 ? "turn off" : "turn on"; }
  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 ); }}