Swing and pattern observer

[dav mrazek]

Hello i would like to have opinion on the way i design my application.
The main frame of the application is containing a JList. Via a JDialog i create new Database object that are displayed in the JList as they are created. I update the model of the JList using the pattern observer. The model implements an observer interface and the Database implements subject interface. Each time i create a Database object i update the model with addElement(database). Is this a good way of doing in swing or there are better one ? Thank you.

[Stan James]

It's common to build a Controller class that is separate from the UI and isn't a Swing component at all. When the user updates a value the View (Swing screen or widget) notifies the Controller. The Controller updates the Model (not the little model inside the Swing control, but a Business Model layer in the application). The observable Model publishes a change event, and other observer widgets on the View listen for that.

Google for MVC and make sure you're reading about fat-client MVC, not web style MVC 2. Let us know what questions all that raises.

This gets a little confusing because Swing has "model" objects and actually has a tiny little MVC architecture going on inside its widgets. For this conversation because you mentioned "database" I'm trying to ignore the little MVC inside Swing and think about a larger application design.

[dav mrazek]

Alright, i m reading this tutorial which is quite clear, but should i have different controller for different object of the model or different ui component, or just one controller for the whole application ?

[dav mrazek]

Hello, i m really having trouble to understand and implements the mvc pattern in my application. If someone could help me to define the view, the controler and the model and how they can interact each other.
So i have Database object that are created through a popup. When i click on a button after filling details of the database, the Database object is instanciated, the popup is not visible and a JList on the main panel is updated with the new database created. The JList model (extends DefaultListModel) contains the list of database objects.
Thanks for help.

[dav mrazek]

Here is what i did based on different tutorial i have read, but i dont feel that i really implemented mvc.
The controller

   public class DatabaseController {
 
    private static List<Database> databases = new ArrayList<Database>();
    private static DefaultListModel listeDBModel;
 
    static {
        logger.debug("static : initialisation liste database");
        for (DBType dbType : DBType.databaseTypes()) {
            if (new File(dbType.propertiesFile()).exists()) {
                logger.debug("File exists - load properties file : " + dbType.propertiesFile());
                Database database = loadProperties(dbType);
                logger.debug("Database loaded : " + database);
                databases.add(database);
                logger.debug("Database list size : " + databases.size());
            }
        }
    }
    
    public DatabaseController(DefaultListModel model) {
        listeDBModel = model;
    }
   
    public static void createDatabase(Database db) {
        databases.add(db);
        listeDBModel.addElement(db);
    }
 
} 

Here is the action that displays the popup :

  @Action
    public void showDBWizard() {
        if (dbWizard == null) {
            JFrame mainFrame = DBApp.getApplication().getMainFrame();
            dbWizard = new DBWizard(mainFrame);
            dbWizard.setLocationRelativeTo(mainFrame);
        }
        DatabaseController controller = new DatabaseController((DefaultListModel)listDB.getModel());
        DBApp.getApplication().show(dbWizard);
    }  

And here is the action that is called when i click on the create button in my popup.

 @Action
    public void createDatabase() {
       //...some code here for checking null or empty value.
        } else  {
            Database db = 
                new Database(
                (DBType)comboDBType.getSelectedItem(), 
                txtDriverFile.getText(), 
                txtJDBCDriverClass.getText(), 
                txtURL.getText(), txtUser.getText(), 
                txtPwd.getPassword());
            db.saveProperties();
            DatabaseController.createDatabase(db);
            setVisible(false);
        }
    }   

[ December 09, 2007: Message edited by: dav mrazek ]

[mandlar suurla]

I am sorry for upping old thread, but i try to implement also MVC pattern in my Swing app. So i made simple examples which should follow simple rules, like all are independent.

Model

package myTemperatureExample;
 
import java.util.Observable;
 
public class Temperature extends Observable {
 
private int temp;
 
public Temperature() {
this.temp = 0;
}
 
public Temperature(int temp) {
this.temp = temp;
}

public int getTemp() {
return temp;
}
 
public void setTemp(int temp) {
this.temp = temp;
setChanged();
notifyObservers();
}

}

Controller and View. As you can see the controller is inner class which you can make as separate class also you can add sub-controllers, like you got there 5 buttons and all are doing something difficult, you can actually make sub-controllers for that.

One thing what i think should be done a bit differently. View should be class which extends from JPanel and then make the Application creation class where you add view. What you think ?

 
package myTemperatureExample;
 
import java.awt.BorderLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.util.Observable;
import java.util.Observer;
 
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JTextField;
 

public class TemperatureGUI extends JFrame implements Observer {
 
JButton addButton;
JButton removeButton;
JTextField textfield;
Temperature t;

public TemperatureGUI() {
Controller c = new Controller();

JPanel mainPanel = new JPanel(new BorderLayout());

addButton = new JButton("Add");
addButton.setActionCommand("ADD");
addButton.addActionListener(c);

removeButton = new JButton("Remove");
removeButton.setActionCommand("REMOVE");
removeButton.addActionListener(c);

textfield = new JTextField(10);

t = new Temperature();
t.addObserver(this);
t.setTemp(38);

mainPanel.add(addButton, BorderLayout.NORTH);
mainPanel.add(removeButton, BorderLayout.SOUTH);
mainPanel.add(textfield, BorderLayout.CENTER);

getContentPane().add(mainPanel);
setSize(150, 150);
}

@Override
public void update(Observable ob, Object obj) {
if (ob instanceof Temperature) {
textfield.setText(Integer.toString(t.getTemp()));
}
}

private class Controller implements ActionListener {

@Override
public void actionPerformed(ActionEvent e) {
String command = e.getActionCommand();
int currentTemp = t.getTemp();

if (command == "ADD") {
currentTemp++;
t.setTemp(currentTemp);

} else if (command == "REMOVE") {
currentTemp--;
t.setTemp(currentTemp);
}
System.out.println("Temp set to:" + t.getTemp());
}
}

public static void main(String[] args) {
javax.swing.SwingUtilities.invokeLater(new Runnable() {
@Override
public void run() {
new TemperatureGUI().setVisible(true);
}
});
}
 
}