Events

The 1.02 model

• All events are handled by handleEvent()
• Events are performed by overriding events like mouseDown(), keyDown(), etc.
• Problems:
  • No way to know which events generated by which components
  • Different components use different fields of the event object

The 1.1 Model

• Components "register" with objects which listen for changes
• Listener objects are responsible for handling the event
• Basic ideas:
  • Every event has a source ( getSource() )
  • Every AWT event has type value ( getID() )
• The event source maintains a list of event listeners that are interested in being notified
• Adapters are overridable methods for events (MouseListener)

Actions

• Give programmers the ability to package commonly used events
• The actions can be shared among containers like JMenus, JPopupMenus, JToolbars, etc.
• Disabling an action disables it everywhere through PropertyChangeEvents

Here are our actions:

// NewAction.java
import java.awt.event.ActionEvent;
import javax.swing.*;

public class NewAction extends AbstractAction {
   MiniEdit theApp;

   public NewAction(MiniEdit theApp) {
      super("New", new ImageIcon("images/new.gif"));
      this.theApp = theApp;
   }

   public void actionPerformed(ActionEvent event) {
      theApp.addToDesktop(new EditFrame());
   }
}

// OpenAction.java
import java.awt.event.ActionEvent;
import javax.swing.*;

public class OpenAction extends AbstractAction {
   MiniEdit theApp;

   public OpenAction(MiniEdit theApp) {
      super("Open", new ImageIcon("images/open.gif"));
      this.theApp = theApp;
   }

   public void actionPerformed(ActionEvent event) {
      JFileChooser chooser = new JFileChooser();
      int option = chooser.showOpenDialog(theApp);
      if (option == JFileChooser.APPROVE_OPTION) {
         System.out.println("You opened " +
             chooser.getSelectedFile().getName());
      } else {
         System.out.println("You canceled.");
      }
   }
}

//QuitAction.java
import java.awt.event.ActionEvent;
import javax.swing.*;

public class QuitAction extends AbstractAction {
   MiniEdit theApp;

   public QuitAction(MiniEdit theApp) {
      super("Quit");
      this.theApp = theApp;
   }

   public void actionPerformed(ActionEvent event) {
      theApp.quit();
   }
}