JavaBeans support

This module contains classes that you can use to add support for bound properties in your classes. This includes being able to add/remove property change listeners, and firing property change events when the attribute values change.

There are two ways to do this:

• Inherit from a class that has the necessary addPropertyChangeListener and removePropertyChangeListener methods (like a Swing component, or JavaBeanSupport) and add the properties you want to fire change events as BeanProperty attributes

  OR

• Inherit from the AutoChangeNotifier mix-in class

Both approaches have their pros and cons, which are detailed below.

BeanProperty

This is a descriptor class that should be installed as a class attribute in a new-style object (one that inherits from object). It handles getting and setting the value, and fires a property change event when the value is set. It requires that the containing class supports property change events (via the add/remove methods mentioned above).

Example:

from swingutils.beans import JavaBeanSupport, BeanProperty

class JustSomeBean(JavaBeanSupport):
    foo = BeanProperty('foo')
    bar = BeanProperty('bar', 'the initial value')

bean = JustSomeBean()
bean.bar = 'the next value'     # Would fire a property change event

Pros:

• Fine grained, can be set up one property at a time
• Plays well together with superclasses that already support bound properties

Cons:

• Cumbersome if you want to make all properties in a class fire property change events

AutoChangeNotifier

This is a mix-in class that works by providing a special method, __setattr__, that catches any attempts to set the value of an attribute. It stores the old value, sets the new attribute value, and then fires a property change event. Private and protected attributes (names starting with _) are excluded from this behavior.

Example:

from swingutils.beans import AutoChangeNotifier

class JustSomeBean(AutoChangeNotifier):
    foo = None
    bar = 'the initial value'

bean = JustSomeBean()
bean.bar = 'the next value'     # Would fire a property change event

Pros:

• Easy to set up, just inherit from it and you’re good to go
• Works for all public properties without extra configuration

Cons:

• May conflict with an existing __setitem__ method
• Coarse grained – can’t choose which public attributes to fire events for