[Chapter 10] 10.8 Defining a Bean Customizer

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| Chapter 10 Java Beans |

## 10.8 Defining a Bean Customizer

A bean may want to provide some way for the user of a beanbox program to customize its properties other than by setting them one at a time. A bean can do this by creating a `Customizer` class for itself, and registering the customizer class with the `BeanDescriptor` object returned by its `BeanInfo` class, as we saw in Example 10.5.

A customizer must be some kind of AWT component that is suitable for display in a dialog box created by the beanbox. Therefore, a customizer class is typically a subclass of `Panel`. In addition, a customizer must implement the `Customizer` interface. This interface consists of methods for adding and removing property change event listeners and a `setObject()` method that the beanbox calls to tell the customizer what bean object it is customizing. Whenever the user makes a change to the bean through the customizer, the customizer should send a `PropertyChangeEvent` to any interested listeners. Finally, like a property editor, a customizer must have a no-argument constructor, so it can easily be instantiated by a beanbox.

Example 10.8 shows a customizer for our `YesNoDialog` bean. This customizer displays a panel that has the same layout as a `YesNoDialog`, but it substitutes a `TextArea` object for the message display and three `TextField` objects for the three buttons that the dialog can display. These text entry areas allow the user to enter values for the `message`, `yesLabel`, `noLabel`, and `cancelLabel` properties. Figure 10.3 shows this customizer panel displayed within a dialog box created by the beanbox program. Again, note that the Done button is part of the beanbox dialog, not part of the customizer itself.

#### Figure 10.3: The customizer dialog for the YesNoDialog bean

#### Example 10.8: The YesNoDialogCustomizer Class

    package oreilly.beans.yesno;
    import java.awt.*;
    import java.awt.event.*;
    import java.beans.*;
    /**
     * This class is a customizer for the YesNoDialog bean.  It displays a
     * TextArea and three TextFields where the user can enter the dialog message
     * and the labels for each of the three buttons.  It does not allow the
     * dialog title or other resources to be set.
     */
    public class YesNoDialogCustomizer extends Panel
                                       implements Customizer, TextListener
    {
      protected YesNoDialog bean;                 // The bean being customized.
      protected TextComponent message, fields[];  // Components used by customizer
      // Default constructor: YesNoDialogCustomizer() { super(); }
      // The bean box calls this method to tell us what object to customize.
      // This method will always be called before the customizer is displayed,
      // so it is safe to create the customizer GUI here.
      public void setObject(Object o) {
        bean = (YesNoDialog)o;   // Save the object we're customizing.
        // Put a label at the top of the panel.
        this.setLayout(new BorderLayout());
        this.add(new Label("Enter the message to appear in the dialog:"), "North");
        // And a big text area below it for entering the dialog message.
        message = new TextArea(bean.getMessage());
        message.addTextListener(this);
        // TextAreas don't know how big they want to be.  You must tell them.
        message.setSize(400, 200);
        this.add(message, "Center");
        // Then add a row of textfields for entering the button labels.
        Panel buttonbox = new Panel();                     // The row container.
        buttonbox.setLayout(new GridLayout(1, 0, 25, 10)); // Equally spaced items.
        this.add(buttonbox, "South");                      // Put row on bottom.
        // Now go create three TextFields to put in this row.  But actually
        // position a Label above each, so create a container for each
        // TextField+Label combination.
        fields = new TextComponent[3];           // Array of TextFields.
        String[] labels = new String[] {         // Labels for each.
          "Yes Button Label", "No Button Label", "Cancel Button Label"};
        String[] values = new String[] {         // Initial values of each.
          bean.getYesLabel(), bean.getNoLabel(), bean.getCancelLabel()};
        for(int i = 0; i < 3; i++) {
          Panel p = new Panel();                 // Create a container.
          p.setLayout(new BorderLayout());       // Give it a BorderLayout.
          p.add(new Label(labels[i]), "North");  // Put a label on the top.
          fields[i] = new TextField(values[i]);  // Create the text field.
          p.add(fields[i], "Center");            // Put it below the label.
          fields[i].addTextListener(this);       // Set the event listener.
          buttonbox.add(p);                      // Add container to row.
        }
      }
      // Add some space around the outside of the panel.
      public Insets getInsets() { return new Insets(10, 10, 10, 10); }
      // This is the method defined by the TextListener interface.  Whenever the
      // user types a character in the TextArea or TextFields, this will get
      // called.  It updates the appropriate property of the bean and fires a
      // property changed event, as all customizers are required to do.
      // Note that we are not required to fire an event for every keystroke.
      // Instead we could include an "Apply" button that would make all the
      // changes at once, with a single property changed event.
      public void textValueChanged(TextEvent e) {
        TextComponent t = (TextComponent)e.getSource();
        String s = t.getText();
        if (t == message) bean.setMessage(s);
        else if (t == fields[0]) bean.setYesLabel(s);
        else if (t == fields[1]) bean.setNoLabel(s);
        else if (t == fields[2]) bean.setCancelLabel(s);
        listeners.firePropertyChange(null, null, null);
      }
      // This code uses the PropertyChangeSupport class to maintain a list of
      // listeners interested in the edits we make to the bean.
      protected PropertyChangeSupport listeners = new PropertyChangeSupport(this);
      public void addPropertyChangeListener(PropertyChangeListener l) {
        listeners.addPropertyChangeListener(l);
      }
      public void removePropertyChangeListener(PropertyChangeListener l) {
        listeners.removePropertyChangeListener(l);
      }
    }

Defining a Complex Property Editor |  | Naming Patterns and Conventions