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To get the most out of this section, read the following documentation:
- Section 7.2 of the JavaBeans API Specification
IndexedPropertyDescriptor
classPropertyEditor
interfacePropertyEditorSupport
classIndexed properties represent collections of values accessed, like an array, by index. The indexed property design patterns are
Conforming to these patterns lets builder tools know that your Bean contains an indexed property.//Methods to access the entire indexed property array public <PropertyType>[] get<PropertyName>(); public void set<PropertyName>(<PropertyType>[] value); //Methods to access individual values public <PropertyType> get<PropertyName>(int index); public void set<PropertyName>(int index, <PropertyType> value);The
OurListBox
demo Bean illustrates how to use an indexed property.OurListBox
extends theList
class to provide a Bean that presents the user with a list of choices: Choices that you can provide and change at design time. Here's an illustration of anOurListBox
instance:OurListBox
exposes theitem
indexed property with the following accessor methods:public void setItems(String[] indexprop) { String[] oldValue=fieldIndexprop; fieldIndexprop=indexprop; populateListBox(); support.firePropertyChange("items",oldValue, indexprop); } public void setItems(int index, String indexprop) { String[] oldValue=fieldIndexprop; fieldIndexprop[index]=indexprop; populateListBox(); support.firePropertyChange("Items",oldValue, fieldIndexprop); } public String[] getItems() { return fieldIndexprop; } public String getItems(int index) { return getItems()[index]; }When an item is set by one of the
setItems()
methods,OurListBox
is populated with the contents of aString
array.Indexed properties are almost as easily exposed to builder tools as simple properties. Writing an indexed property editor, though, requires writing a custom property editor.
The
OurListBox
demo Bean provides an associatedIndexPropertyEditor
which is a good example of how to implement an indexed property editor. The following illustration shows anOurListBox
instance in the BeanBox, the Properties sheet which contains an entry for the indexed propertyitems
, and theIndexPropertyEditor
which pops up when theitems
property entry is clicked:
This figure has been reduced to fit on the page.
Click the image to view it at its natural size.Implementing
IndexPropertyEditor
is the same as implementing any custom property editor:
- Implement the
PropertyEditor
interface:You can use thepublic class IndexPropertyEditor extends Panel implements PropertyEditor, ActionListener {PropertyEditorSupport
class, either by subclassing or as an inner class.- Denote the custom editor in a related
BeanInfo
class.OurListBox
has a relatedOurListBoxBeanInfo
class that contains the following code:itemsprop.setPropertyEditorClass( IndexPropertyEditor.class);
- Make the property editor a source for bound property events. The property editor will register property listeners, and fire property change events at those listeners. This is how the property changes are propagated back to the Bean (via the property sheet). So
IndexPropertyEditor
instantiates an innerPropertyChangeSupport
class:Provides the ability for objects to register their interest in being notified when a property is edited:private PropertyChangeSupport support = new PropertyChangeSupport(this);And fires property change events at those listeners:public void addPropertyChangeListener( PropertyChangeListener l) { support.addPropertyChangeListener(l); } public void removePropertyChangeListener( PropertyChangeListener l) { support.removePropertyChangeListener(l); }public void actionPerformed(ActionEvent evt) { if (evt.getSource() == addButton) { listBox.addItem(textBox.getText()); textBox.setText(""); support.firePropertyChange("", null, null); } else if (evt.getSource()== textBox) { listBox.addItem(textBox.getText()); textBox.setText(""); support.firePropertyChange("",null,null); } ... }
IndexPropertyEditor
maintainslistbox
as a proxy forOurListBox
. When a change is made tolistbox
, a property change event is fired to all listeners.When the Properties sheet, which is registered as an
IndexPropertyEditor
listener, receives a property change event fromIndexPropertyEditor
, the Properties sheet callsIndexPropertyEditor.getValue
to retrieve the new or changed items and update the Bean.
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